FROM CINDER CONES TO SUBDUCTION ZONES: VOLATILE … · Ikuko Wada, Dominique Weis, Dan Rasmussen,...
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FROM CINDER CONES TO SUBDUCTION ZONES: VOLATILE RECYCLING AND MAGMA FORMATION BENEATH THE SOUTHERN CASCADE ARC by KRISTINA JANINE WALOWSKI A DISSERTATION Presented to the Department of Geological Sciences and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 2015
Transcript of FROM CINDER CONES TO SUBDUCTION ZONES: VOLATILE … · Ikuko Wada, Dominique Weis, Dan Rasmussen,...
FROM CINDER CONES TO SUBDUCTION ZONES: VOLATILE RECYCLING AND
MAGMA FORMATION BENEATH THE SOUTHERN CASCADE ARC
by
KRISTINA JANINE WALOWSKI
A DISSERTATION
Presented to the Department of Geological Sciences
and the Graduate School of the University of Oregon
in partial fulfillment of the requirements
for the degree of
Doctor of Philosophy
June 2015
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DISSERTATION APPROVAL PAGE
Student: Kristina Janine Walowski
Title: From Cinder Cones to Subduction Zones: Volatile Recycling and Magma
Formation beneath the Southern Cascade Arc
This dissertation has been accepted and approved in partial fulfillment of the
requirements for the Doctor of Philosophy degree in the Department of Geological
Sciences by:
Dr. Paul Wallace Chairperson
Dr. Ilya Bindeman Core Member
Dr. Gene Humphreys Core Member
Dr. Darren Johnson Institutional Representative
and
Scott L. Pratt Dean of the Graduate School
Original approval signatures are on file with the University of Oregon Graduate School.
Degree awarded June 2015
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© 2015 Kristina Janine Walowski
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DISSERTATION ABSTRACT
Kristina Janine Walowski
Doctor of Philosophy
Department of Geological Sciences
June 2015
Title: From Cinder Cones to Subduction Zones: Volatile Recycling and Magma
Formation beneath the Southern Cascade Arc
Volatiles (H2O, CO2, S, Cl) play a key role in magmatic processes at subduction
zones. In this study, the dissolved volatile contents of olivine-hosted melt inclusions from
cinder cones in the Lassen segment of the Cascade arc are used to investigate dehydration
of subducted oceanic lithosphere, magma formation in the sub-arc mantle wedge, and
mafic magma storage and evolution in the crust.
Relatively young, hot oceanic lithosphere subducts beneath the Cascade arc. The
hydrogen-isotope and trace-element compositions of melt inclusions, when integrated
with thermo-petrologic modeling, demonstrate that fluids in Cascade magmas are sourced
from hydrated peridotite in the deep slab interior and that the oceanic crustal part of the
slab extensively dehydrates beneath the forearc. In contrast to their slab-derived H, the
melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean
ridge basalt (MORB), requiring little to no slab contribution of B, which is also consistent
with extensive dehydration of the downgoing plate before it reaches sub-arc depths.
Correlations of volatile and trace element ratios in the melt inclusions (H2O/Ce, Cl/Nb,
Sr/Nd) demonstrate that geochemical variability in the magmas is the result of variable
amounts of addition of a hydrous subduction component to the mantle wedge. Radiogenic
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isotope ratios require that the subduction component has less radiogenic Sr and Pb and
more radiogenic Nd than the Lassen sub-arc mantle and is therefore likely to be a partial
melt of subducted Gorda MORB. These results provide evidence that chlorite-derived
fluids from the deep slab interior flux-melt the oceanic crust, producing hydrous slab
melts that migrate into the overlying mantle, where they react with peridotite to induce
further melting.
The basaltic magmas that erupted at Cinder Cone near Mt. Lassen trapped melt
inclusions during olivine crystallization at ~7-15 km depth. The melt inclusion
compositions require that two different mantle-derived magmas were involved in the
eruption, and temporal changes show that arrival of the two batches correlates with two
explosive phases of activity. Both magmas experienced rapid crustal contamination
before erupting, illustrating the complexities of cinder cone eruptions.
This dissertation includes previously published and unpublished co-authored
material.
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CURRICULUM VITAE
NAME OF AUTHOR: Kristina Janine Walowski
GRADUATE AND UNDERGRADUATE SCHOOLS ATTENDED:
University of Oregon, Eugene
University of California, Los Angeles
DEGREES AWARDED:
Doctor of Philosophy, Geological Sciences, 2015, University of Oregon
Bachelor of Science, Geology, 2015, University of California, Los Angeles
AREAS OF SPECIAL INTEREST:
Geochemistry, Petrology, Volcanology
PROFESSIONAL EXPERIENCE:
Graduate Teaching Fellow (2010-2015).
University of Oregon, Department of Geological Sciences
Research Assistant (2011-2015)
University of Oregon, Department of Geological Sciences
Advisor: Paul Wallace
Undergraduate Research Assistant (2008-2010)
University of California, Los Angeles, Department of Earth and Space
Sciences
Advisor: Jeremy Boyce
GRANTS, AWARDS, AND HONORS:
GeoPRISMS AGU Student Prize for Best Oral Presentation (2014).
McMurray Award (2014). Department of Geological Science, University of
Oregon.
Goldschmidt Student Travel Grant (2013). Geochemical Society.
Graduate Research Award (2013). Graduate School, University of Oregon.
GeoPRISMS AGU Student Prize Honorable Mention (2012).
Staples Scholarship (2012). Department of Geological Science, University of
Oregon.
Valedictorian (2010), Department of Earth and Space Sciences, University of
California, Los Angeles.
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PUBLICATIONS:
Walowski, K. J., Wallace, P. J., Hauri, E. H., Wada, I., & Clynne, M. A. (2015).
Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic
peridotite. Nature Geoscience, 8(5), 404-408.
Walowski K, Wallace P, Clynne M. (2014). Slab Melting and Magma Formation
beneath the southern Cascade Arc. AGU Fall Meeting Abstracts, V31G-03.
Walowski K, Wallace P, Hauri E, Clynne M & Wada I (2014). Slab Dehydration
beneath the Southern Cascade Arc Inferred from B and H Isotopes. Goldschmidt Abstracts,
2014, 2613.
Walowski, K. J., Wallace, P. J., Hauri, E. H., Clynne, M. A., Rea, J., &
Rasmussen, D. J. (2013). Magma formation in hot-slab subduction zones: Insights from
hydrogen isotopes in Cascade Arc melt inclusions. In AGU Fall Meeting Abstracts (Vol.
1, p. 01).
Walowski K, Wallace P, Clynne M, Wada I & Rasmussen D (2013). Magma
Formation in Hot-Slab Subduction Zones: Insights from Volatile Contents of Melt Inclusions
from the Southern Cascade Arc. Mineralogical Magazine, 77(5), 2441.
Walowski K, Wallace P, Clynne M, Wada I & Rasmussen D (2012). Understanding magma formation and mantle conditions in the Lassen segment of the Cascade
Arc: Insights from volatile contents of olivine-hosted melt inclusions. AGU Fall Meeting
Abstracts, V14B-01.
Walowski, K. J., Wallace, P. J., Cashman, K. V., & Clynne, M. A. (2011).
Inferring the magmatic plumbing system and melt evolution from olivine-hosted melt
inclusions at Cinder Cone, Lassen Volcanic National Park, California. In AGU Fall
Meeting Abstracts (Vol. 1, p. 02).
Walowski, K. J., and Boyce, J.W. (2009). Volatile History of the Bishop Tuff from
Apatite Phenocrysts and Inclusions. AGU Fall Meeting Abstracts,V23C-2093.
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ACKNOWLEDGMENTS
This dissertation has benefited from the contributions of many people. First, I
would like to thank my advisor, Paul Wallace, for his guidance and support throughout
my Ph.D. I can’t imagine a better Ph.D. advisor, and I am privileged to have gotten the
opportunity to work with him. I’d also like to thank the faculty at the University of
Oregon, and specifically, my dissertation committee members, Ilya Bindeman for
teaching me about isotopes, Gene Humphreys for helping me see the bigger picture, and
Darren Johnson. My dissertation benefited from a number of collaborations, and includes
the contributions of many co-authors, apart from Paul and myself. Thanks to Erik Hauri,
Ikuko Wada, Dominique Weis, Dan Rasmussen, Kathy Cashman, Katie Marks, and
Philipp Ruprecht for their individual contributions, and John Donavan, Adam Kent, and
Brian Monteleone for their assistance with various analytical instruments. In particular, I
would like to thank Mike Clynne, whose Ph.D. thesis and continued work in the Lassen
area laid the foundation my dissertation research, and for his important contributions to
all three chapters.
This work was largely funded by the National Science Foundation through research
grants awards to Paul Wallace and Kathy Cashman (EAR-1019848 and EAR-1119224).
I’d also like to thank the incredible graduate community that I was so lucky be a
part of. To the few who were there from start to finish – Kristin Sweeney, Corina
Cerovski-Darriau, and Scott Maguffin – we’ve had a great run, and I hope it doesn’t end
here! Special thanks to Angie Seligman, who the first floor would not have been the same
without, Randy Krogstad, who will always be one of my best friends, Amberlee Darold
and Gillean Arnoux, who made Cascade 124 a better place, and, of course, Captain
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Malcom Reynolds.
I’d also like to specially thank my first academic ‘dad’, Jeremy Boyce. He inspired
me to follow this path and prepared me so well for the journey that has been my Ph.D.
Five years later, he is still there for me whenever I need advice and guidance, which is
something I truly value.
To my Mom and Dad, I could never thank you enough for your unconditional love
and support. You have both taught me so much, and given me everything I could have
ever needed. It is difficult to put into words how much you both mean to me, and I love
you both very much. To my brother, Chris, thank you for showing me the coolness of
science. I truly value our friendship and look forward to joining you in the higher-ed
scientist club. Finally, I’d like to thank my partner Alexander Handwerger, without
whom none of this would have been possible. Thank you for being there for me every
single step of the way, and bringing me so much happiness. Our time in Oregon has been
incredible, and I can’t wait to start our next adventure together in Scotland!
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To My Family
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TABLE OF CONTENTS
Chapter Page
I. INTRODUCTION .................................................................................................... 1
1.1. Water, Subduction, and the Cascade Arc ........................................................ 1
1.2. Scientific Approach ........................................................................................ 2
1.3. Dissertation Organization ............................................................................... 3
II. SLAB MELTING BENEATH THE CASCADE ARC DRIVEN BY
DEHYDRATION OF ALTERED OCEANIC PERIDOTITE .............................. 7
2.1. Introduction ..................................................................................................... 7
2.2. Slab Surface Temperatures ............................................................................. 11
2.3. Hydrogen Isotopes .......................................................................................... 13
2.4. D/H Fractionation Model ................................................................................ 15
2.5. Evidence and Implications for Slab Melting .................................................. 18
2.6. Bridge .............................................................................................................. 20
III. SLAB MELTING AND MAGMA FORMATION BENEATH THE
SOUTHREN CASCADE ARC ............................................................................. 21
3.1. Introduction ..................................................................................................... 21
3.2. Geologic Setting.............................................................................................. 24
3.3. Sample Descriptions and Analytical Methods ................................................ 26
3.4. Results ............................................................................................................. 28
3.4.1. Melt Inclusion Major and Trace Element Compositions ....................... 28
3.4.2. Magmatic Volatile Contents .................................................................. 31
3.4.3. Isotopic Compositions ........................................................................... 32
3.5. Discussion ....................................................................................................... 33
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Chapter Page
3.5.1. The Source of Volatiles in the Lassen Region Primitive Magmas ........ 33
3.5.2. Evidence for Slab Melting .................................................................... 37
3.5.3. The Role of Sediment Melts and Crustal Assimilation ......................... 41
3.5.4. Modeling Slab Melt Addition to the Mantle Wedge ............................. 43
3.5.5. The Sr/Y Adakite Signature ................................................................... 47
3.5.6. Model for Melt Generation beneath the Southern Cascade Arc ............ 49
3.6. Conclusions ..................................................................................................... 52
3.7. Bridge .............................................................................................................. 53
IV. UNDERSTANDING MELT EVOLUTION AND THE MAGMATIC
PLUMBING SYSTEM AT CINDER CONE, LASSEN VOLCANIC
NATIONAL PARK CALIFORNIA: INSIGHTS FROM
OLIVINE-HOSTED MELT INCLUSIONS.......................................................... 54
4.1. Introduction ..................................................................................................... 54
4.2. Geologic Setting.............................................................................................. 58
4.3. Sample Descriptions and Tephra Stratigraphy ............................................... 59
4.4. Methods........................................................................................................... 63
4.4.1. Sample Preparation ................................................................................ 63
4.4.2. Analytical Procedures ............................................................................ 64
4.5. Results ............................................................................................................. 66
4.5.1. Olivine Compositions ............................................................................ 66
4.5.2. Post-entrapment Crystallization and Fe-loss Corrections ...................... 67
4.5.3. Major Element Compositions ................................................................ 68
4.5.4. Volatile Concentrations ......................................................................... 70
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Chapter Page
4.5.5. Trace Element Concentrations ........................................................................... 75
4.6. Discussion ....................................................................................................... 76
4.6.1. Crustal Contamination at Cinder Cone .................................................. 76
4.6.2. Parental Melt Compositions ................................................................... 79
4.6.3. Timescales of Mixing and Ascent.......................................................... 84
4.6.4. Mechanisms of Crustal Contamination and
Plumbing System Evolution ................................................................ 87
4.7. Conclusions ..................................................................................................... 91
APPENDICES ............................................................................................................. 93
A. CHAPTER II SUPPLEMENTARY MATERIALS .......................................... 93
A.1. Methods .............................................................................................. 93
A.2. Supplementary Discussion ................................................................. 95
A.3. Hydrogen Isotope and Trace Element Compositions ........................ 113
B. CHAPTER III SUPPLEMENTARY MATERIALS......................................... 125
B.1. Restored Melt Inclusion Compositions .............................................. 125
B.2. Boron Isotope Compositions .............................................................. 134
B.3. Radiogenic Isotope Compositions ...................................................... 135
C. CHAPTER IV SUPPLEMENTARY MATERIALS ........................................ 136
C.1. PEC Corrected Melt Inclusion Compositions .................................... 136
C.2. Analyzed (uncorrected) Melt Inclusion Compositions ...................... 143
REFERENCES CITED ................................................................................................ 149
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LIST OF FIGURES
Figure Page
2.1 Cascade Arc Regional Map and Lassen Sample Locations ................................... 9
2.2 Melt Inclusion Compositions and Slab Surface Temperatures .............................. 13
2.3 Hydrogen Isotopes: Measured Values and Model Results .................................... 17
3.1 Sample Locations and Across-Arc Geochemical Variability ................................ 25
3.2 Corrected Melt Inclusion Major and Trace Element Compositions ...................... 30
3.3 Boron Isotope Compositions.................................................................................. 33
3.4 Corrected Melt Inclusion Volatile and Trace Element Ratios ............................... 36
3.5 Radiogenic Isotope Compositions and Slab Melt Mixing Models ........................ 39
3.6 Percent Melt and source H2O: Results from pMELTS .......................................... 44
3.7 Comparison of pMELTS Model Results and Melt Inclusion Compositions ......... 46
3.8 The Effect of Slab Melt Addition to Peridotite for Sr/Y, Y and H2O .................... 48
3.9 Schematic Interpretation for Magma Formation beneath the S. Cascades ............ 52
4.1 Geologic and Isopach Map of Cinder Cone ........................................................... 60
4.2 Stratigraphic Section of Sample Locality .............................................................. 62
4.3 Olivine Phenocryst Compositions.......................................................................... 67
4.4 Melt Inclusion Total Alkalis and SiO2 Compared to Bulk Tephra and Lava ........ 70
4.5 Melt Inclusion MgO vs. Al2O3 and CaO ............................................................... 71
4.6 Melt Inclusion Corrected H2O vs. CO2 .................................................................. 75
4.7 Spider Diagram of Average Melt Inclusions Compositions .................................. 76
4.8 Modeled Mixing with Granitic Xenoliths .............................................................. 78
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Figure Page
4.9 Melt Inclusion Li vs. Pb ......................................................................................... 80
4.10 Melt Inclusion MgO vs. Trace Elements ............................................................. 82
4.11 Comparison of Cinder Cone to Lassen Region Magmas ..................................... 84
4.12 Ni Diffusion in Olivine ........................................................................................ 86
4.13 Temporal Variability in Bulk Tephra Composition ............................................. 89
4.14 Core to Rim Variations in Olivine Xenocrysts .................................................... 90
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LIST OF TABLES
Table Page
2.1 Average Volatile, Trace Element, and Stable Isotope Compositions of
Melt Inclusions from the Lassen Region Cinder Cones ........................................ 11
3.1 Averaged Primary Melt Compositions .................................................................. 29
4.1 Tephra Stratigraphy and Sample Descriptions ...................................................... 63
1
CHAPTER I
INTRODUCTION
1.1. Water, Subduction, and the Cascade Arc
The distribution of water in the Earth’s mantle has a strong impact on the
evolution of our planet. Introduced to the mantle through subduction, water makes active
plate tectonics possible on Earth by reducing rock viscosities, facilitating mantle
convection (e.g. Jung and Karato, 2001). Melting of the mantle wedge in subduction
zones would not be possible without the addition of water (e.g., Ringwood, 1974), and
once these melts reach the surface, their water contents directly affect the explosivity of
the magma (e.g., Roggensack, 1997; Metrich and Wallace, 2008). The influence water
has on a number of processes, such as the formation of volcanic arcs and production of
continental crust, makes understanding the origins and distribution of water in subduction
zones a very important area of research in the earth sciences.
Perhaps the most important role of H2O in subduction zones is driving magma
production. When the oceanic lithosphere is subducted, increasing temperatures and
pressures cause the progressive breakdown of hydrous phases in a series of reactions that
release H2O into the overlying mantle wedge (e.g., Schmidt and Poli, 1998). In the classic
model of petrogenesis at subduction zones, these aqueous fluids infiltrate the mantle
wedge, lower the solidus, and cause melting. However, convergent margins vary globally
- they subduct oceanic lithosphere of different ages and at different rates (e.g., Syracuse
et al., 2010), and have sediment packages of different thicknesses and compositions (e.g.,
Plank & Langmuir, 1993). Different combinations of plate age and convergence rate
2
control how rapidly temperatures in the slab increase with depth, and therefore influence
the depths at which dehydration reactions occur (e.g., Schmidt & Poli, 1998; Hacker,
2008), and the composition of the fluids and/or melts that infiltrate the mantle wedge
(e.g., Kessel et al., 2005).
The Cascadia subduction zone, which runs from northern California to southern
British Columbia, represents a global endmember, subducting very young oceanic
lithosphere (6-10 Ma at the trench; Wilson et al., 2002, Kirby et al., 2002). The processes
that drive magma formation beneath the Cascade arc and other warm-slab subduction
zones have been debated because young oceanic crust should largely dehydrate beneath
the forearc (Van Keken et al., 2010), where the mantle wedge is not at high enough
temperatures to melt. In addition, geochemical variability along strike in the Cascades has
led to contrasting interpretations about the role of volatiles in magma generation (e.g.,
Leeman et al., 1990; Grove et al., 2002; Ruscitto et al., 2010). In this dissertation, I focus
on the Lassen segment of the Cascade arc, where previous studies have demonstrated that
across-arc geochemical variations in primitive basaltic magmas result from varying
extents of mantle wedge fluxing by material recycled from the slab. Using direct
measurements of dissolved magmatic volatiles and a number of other geochemical tools,
I show how the subduction of warm oceanic lithosphere beneath the Cascades influences
dehydration reactions in the downgoing slab and melt production in the mantle wedge.
1.2. Scientific Approach
Volatiles, such as H2O, CO2, S, Cl, and F, play a key role a number magmatic
processes. Pre-eruptive volatile contents are difficult to estimate, however, because they
3
decrease in solubility as pressure decreases and exsolve from the magma during ascent,
driving explosive eruptions (e.g., Roggensack, 1997; Metrich and Wallace, 2008). As a
result, most magmatic volatiles are lost to the atmosphere, leaving the resulting volcanic
material with only a small fraction of the volatile contents with which it began (e.g.,
Holloway and Blank, 1994). In this dissertation, I utilize the geochemistry of melt
inclusions hosted in olivine crystals to get around this problem. Melt inclusions are small
volumes of melt trapped inside of phenocrysts at depth. Olivine-hosted melt inclusions
are one of the best tools currently available to directly measure pre-eruptive volatile
concentrations, because they are often trapped at depth, before significant degassing
occurs (Anderson, 1974; Schiano, 2003). Because they are trapped at depth, they not
only provide estimates of pre-eruptive volatiles, but may also provide a unique snapshot
of melt compositions, before magmatic evolution occurs.
1.3. Dissertation Organization
This dissertation is separated into three stand-alone chapters that are prepared as
individual manuscripts for publication. Chapters II and III investigate deep magmatic
processes, such as mantle melting and slab recycling, while Chapter IV focuses on
shallow (crustal level) magmatic processes that occur prior to and during cinder cone
eruptions. The unifying theme of the dissertation is the use of melt inclusions in olivine
sampled from tephra deposits at mafic cinder cones. Throughout the dissertation, I show
that melt inclusion datasets can be utilized to answer a wide range of questions when
integrated with other types of data (e.g., radiogenic isotopes, mineral chemistry, eruptive
4
stratigraphy) and modeling (e.g., geodynamic, geochemical, and thermodynamic
modeling).
In Chapter II, “Slab Melting beneath the Cascade Arc driven by dehydration of
altered oceanic peridotite,” I use the hydrogen isotope composition of basaltic melt
inclusions from seven different cinder cones to fingerprint the fluid sources that initiate
magma generation beneath the Cascade arc. I also develop a thermo-petrologic model to
calculate progressive D/H fractionation in the subducting plate to inform the geochemical
data. The results show that the downgoing plate beneath the southern Cascades
experiences extensive dehydration and that fluids derived from the slab interior may flux-
melt the slab top. In Chapter III, “Slab Melting and Magma Formation beneath the
Southern Cascade Arc,” I use a larger melt inclusion dataset to further test the
interpretations presented in Chapter II. I use B concentrations and isotope ratios, trace
elements, and the volatile concentrations of the melt inclusions along with the radiogenic
isotope ratios of bulk tephra from the eight different cinder cones (one additional cone to
the seven discussed in Chapter II). This dataset is used to demonstrate that geochemical
variability of primitive basalts in the Lassen region is the result of variable amounts of
addition of a hydrous subduction component to the mantle wedge, and also provides
strong evidence that melting of the subducted basaltic oceanic crust beneath the Lassen
region plays an important role in magma formation in the mantle wedge. The combined
results of Chapters II and III indicate that chlorite-derived fluids from the deep slab
interior can flux-melt the oceanic crust, producing hydrous slab melts that migrate into
the overlying mantle, where they react with peridotite to induce further melting. I suggest
that this mechanism for slab melting and magma formation may be common in arcs
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beneath which young oceanic crust subducts, such as central Mexico (e.g., Cai et al.,
2014).
In Chapter IV, I investigate the compositional evolution of magmas from the
youngest cinder cone in the Cascade arc, Cinder Cone (eruption age 1666 C.E.; Sheppard
et al., 2009). I integrate melt inclusion compositions with stratigraphic information, bulk
lava and tephra compositions, mineral chemistry, and physical volcanology to better
understand the processes and timescales associated with the storage, ascent, and eruption
of magmas at this monogenetic volcano. I find that two different mantle-derived magmas
were tapped during the eruption of Cinder Cone, correlating with two explosive eruptive
phases. Both magmas experienced rapid crustal contamination before erupting at the
surface similar to other well-documented cinder cone eruptions (e.g., Paricutin and
Jorullo, in Meixco; e.g., Pioli et al., 2008, Johnson et al., 2008). However, the timescales
and mechanisms of contamination and eruption are shown to occur more rapidly at
Cinder Cone than monogenetic volcanoes in central Mexico, illustrating the complexities
of short-lived cinder cone eruptions.
For all chapters in this dissertation, I am the first author, and performed all of the
laboratory work, field-based work, and analytical work, unless explicitly stated. Chapter
II has been published in Nature Geoscience with Dr. Paul Wallace (advisor), Dr. Erik
Hauri (Carnegie Instiution of Washington), Dr. Ikuko Wada (University of Minnesota),
and Dr. Michael Clynne (U.S. Geological Survey). Chapter III is in preparation in the
style of Earth and Planetary Science Letters and will be coauthored by Dr. Paul Wallace
(advisor), Dr. Michael Clynne (U.S. Geological Survey), Dan Rassmussen (Ph.D.
candidate, Lamont-Doherty Earth Observatory), and Dr. Dominique Weis (University of
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British Columbia). Chapter IV is in preparation in the style of Bulletin of Volcanology
and will be coauthored by Dr. Paul Wallace (advisor), Dr. Michael Clynne (U.S.
Geological Survey), Dr. Kathy Cashman (University of Bristol), J. Katie Marks (M.S.,
University of Oregon), and Dr. Philipp Ruprecht (Lamont-Doherty Earth Observatory).
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CHAPTER II
SLAB MELTING BENEATH THE CASCADE ARC DRIVEN BY
DEHYDRATION OF ALTERED OCEANIC PERIDOTITE
This work was published in volume 8 of the journal Nature Geoscience in May,
2015. Sample collection was performed by me with the help of Dr. Wallace and Dr.
Clynne. Sample preparation for and Nano-secondary ion mass spectrometry volatile and
hydrogen isotope analyses were performed by me with the help of Dr. Hauri. Data
corrections, analyses, and interpretation were performed by me, with the help of
Dr.Wallace. The fractionation model was created by me with the help of Dr. Wada and
incorporated her previously published work. I drafted all the figures used in this article
and the text was written by me, with editorial assistance by Dr. Wallace.
2.1. Introduction
Water is returned to Earth’s interior at subduction zones. However, the processes
and pathways by which water leaves the subducting plate and causes melting beneath
volcanic arcs are complex; the source of the water—subducting sediment, altered oceanic
crust, or hydrated mantle in the downgoing plate—is debated; and the role of slab
temperature is unclear. Here we analyse the hydrogen-isotope and trace-element
signature of melt inclusions in ash samples from the Cascade Arc, where young, hot
lithosphere subducts. Comparing these data with published analyses, we find that fluids
8
in the Cascade magmas are sourced from deeper parts of the subducting slab—hydrated
mantle peridotite in the slab interior—compared with fluids in magmas from the
Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling
to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly
dehydrates at shallow depths. With continued subduction, fluids released from the deeper
plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn
migrate into the overlying mantle wedge, where they trigger further melting. Our results
provide a physical model to explain melting of the subducted plate and mass transfer
from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is
subducted.
The Cascadia subduction zone and associated magmatic arc in the U.S. and
Canada is a global endmember example of a “warm-slab” subduction zone 1,2
, in which
very young (6-9 Ma at the trench)3 and therefore hot oceanic crust subducts (Fig. 2.1).
Such arcs have proven to be a challenge to our current understanding of arc magmatism
because the hotter nature of the young subducted plate causes most dehydration of the
oceanic crust to occur beneath the forearc rather than the arc4,5
. As a result, little H2O
may reach sub-arc depths to initiate melt production in the overlying mantle wedge,
unless there is substantial H2O carried to greater depths by hydrated (serpentinized)
peridotite in the mantle portion of the downgoing slab6. Basaltic magmas in the Cascades
have H2O contents (3.2 ±1.2 wt%)7,8,9
that are only slightly lower than the global arc
average (3.9±0.45 wt%, 1 s.d.)10
, raising questions about the extent of dehydration of the
subducting plate beneath the forearc and the extent to which hydrated mantle in the
subducting plate carries H2O to sub-arc depths.
9
Figure 2.1. Cascade arc regional map and Lassen sample locations. a) Regional map of
the Northwestern United States showing major tectonic boundaries. Black arrows show
the direction and convergence rate of the Juan de Fuca and Gorda plates. Lassen Peak
(red triangle) represents the southernmost active volcanic center of the Quaternary
Cascade arc. b) Expanded map of the Lassen Region with locations of Quaternary cinder
cones sampled in this study. Symbols and colors for calc-alkaline basalt (CABs; squares)
and CAB-transitional (circles) samples are used throughout the article.
Hydrogen isotopes have a larger mass difference than any other isotope pair, and
as a result, they exhibit strong isotopic fractionation during various geologic processes. In
subduction zones, as hydrous minerals break down with increasing temperature and
10
pressure, the D/H ratio is fractionated, producing D-enriched fluids and a complementary
residual slab that is isotopically lighter11
. Recent work in the Marianas has shown that
because the contribution of D and H from the overlying mantle is minimal, the δD
signature (δD=1,000×[(D/H)sample − (D/H)SMOW] /(D/H)SMOW, where SMOW is standard
mean ocean water with δD=0) of slab fluids may be retained in primitive arc magmas11
.
This makes magmatic D/H ratios a valuable tool for investigating volatile recycling in the
Cascade arc because the thermal structure of the slab strongly influences the depths at
which key dehydration reactions occur in the downgoing plate6,12
.
Here we focus on the Lassen segment of the Cascade arc, the southernmost active
segment of the arc, where previous work has shown across-arc geochemical variations
related to subduction enrichment13,14
(Fig. 2.1a). Our samples were collected from tephra
deposits associated with primitive basaltic cinder cones (MgO > 7 wt%; Supplementary
Table A.1; see Appendix A for all supplementary information for this chapter), which
span ~80 km across the arc axis (Fig. 2.1b). Melt inclusions – glassy “blobs” of silicate
melt trapped inside olivine crystals – were used in this study to measure pre-eruptive
volatile contents. We present the analyses of melt inclusions from four calc-alkaline
basalts (CAB) and three basalts that are transitional between CAB and low-K tholeiite
(LKT) based on trace element patterns (Supplementary Fig. A.1). Using the maximum
volatile contents at each cone to represent the undegassed magma, we find values of 2.47-
3.4 wt% H2O for CABs and 1.3-1.4 wt% H2O for transitional CABs in the Lassen region
(Table 2.1). The CAB values are similar to H2O contents of other Cascade CAB
magmas7,8,9
, whereas the transitional CABs have lower values, as expected, given that
11
they are transitional towards LKTs, which are interpreted to be relatively dry magmas
formed by decompression melting15
.
Table 2.1. Average volatile, trace element and stable isotope composition of melt
inclusions from Lassen Region cinder cones.
In addition to H2O, trace element ratios of large ion lithophile elements (LILE)
and light rare earth elements (LREE) are also commonly used to distinguish addition of a
hydrous subduction component to the mantle source because of the fluid mobility of
LILEs and relative depletion of LREE in the mantle wedge. In the Lassen region, (Sr/P)N
(N refers to normalization to primitive mantle16
) has been used to distinguish a
subduction component because it correlates with LILE/LREE ratios and varies
systematically across the arc13,14
. For magmas from the Lassen region, (Sr/P)N correlates
with other slab component tracers such as H2O/Ce (Fig. 2.2a), demonstrating a clear link
between volatile and trace element enrichment of the mantle wedge as the result of
variable addition of a hydrous slab component.
2.2. Slab Surface Temperatures
To better understand thermal conditions at the slab-wedge interface, we
developed a 2-D steady-state thermal model for this region2. The maximum depth of slab-
12
mantle decoupling (MDD) controls the trench-ward extent of solid mantle wedge flow,
and this depth tends to be 70-80 km for most subduction zones2. In our model for the
Lassen segment, we assume that the MDD is 75 km. Temporal changes in regional
tectonics or slab geometry can cause deviation from the common MDD. Thus, the range
of slab surface temperatures predicted by models with MDD of 65–85 km depth are
shown in Figure 2.2b. We also calculated slab surface temperatures using the H2O/Ce
ratio17
(see Supplementary Information A.) as an independent comparison with the
thermal model. Slab surface temperatures at sub-arc depths of ~85-95 km18
beneath the
Lassen segment calculated using this method are 725-850 ± 50 °C (Fig. 2.2b), slightly
lower than temperatures predicted by the thermal model. Our thermal model does not
include the effects of fluid circulation within the oceanic crust at shallow depths in the
subduction zone or the latent heat of fusion that would affect temperatures if the oceanic
crust at the plate top was partially melted (see Supplementary Information A.2). Each of
these effects could reduce the slab surface temperatures by ~50 °C19
. Furthermore, in
interpreting H2O/Ce temperatures, we neglect the potential effects of lateral migration of
fluids and melts through the wedge20
which may contribute to the difference between the
two estimates (see Supplementary Information A.2). Regardless of the small offset, both
the thermal model and H2O/Ce temperature estimates indicate active fluxing of hydrous
material from the slab into the mantle wedge beneath the arc rather than down-dragging
of hydrous mantle from the forearc region. If the latter was an important process, it
would have imprinted the mantle wedge with relatively high H2O/Ce, resulting in lower
apparent temperatures17
. Calculated slab surface temperatures beneath the Cascades
(from both methods) also plot at or above the solidi of both mid-ocean ridge basalt
13
(MORB)+H2O21
and sediment+H2O22
(Fig. 2.2b), indicating the likelihood of partial
melting of the slab top if H2O is present.
Figure 2.2. Melt inclusion compositions and slab surface temperatures. a) H2Omax/Ce
versus (Sr/P)N for least degassed melt inclusions. 10% partial melts of depleted mantle
(DMM)46
and more enriched mantle47
(E-M; 66% DMM and 33% E-M; see
Supplementary Fig. A.2 and Information) mixed with a hydrous component were used to
calculate curves, labeled with the % of total H2O contributed by the subduction
component in the final magma. b) Slab surface temperatures from the H2O/Ce
thermometer17
, 2-D thermal model for the Lassen segment (MDD of 75 km; solid black
curve), and the sediment + H2O 22
and MORB + H2O solidi21
. Temperatures predicted by
thermal models with MDDs of 65–85 km shown by grey shaded region.
2.3. Hydrogen Isotopes
The melt inclusion data from the Lassen region show a negative correlation
between measured δD values and H2O (Supplementary Fig. A.3). Recent experimental
work demonstrates that this correlation is the result of post-entrapment fractionation
caused by preferential diffusive loss of H relative to D through the olivine host23, 24
, and
14
our data show the first evidence for this process in naturally glassy samples
(Supplementary Fig. A.3). Using a diffusive re-equilibration model24
, we calculated the
initial δD composition for each cone by assuming that the highest H2O concentrations
measured are in melt inclusions that are least affected by this process (Supplementary
Fig. A.3). We compare our results (Fig. 2.3a) with published data from the Marianas11
where negative correlations between δD and H2O wt% are not observed. The Marianas
data come from longer-lived volcanoes that erupted more explosively, and diffusive H
loss may have been minimized by rapid ascent rates and lower magmatic temperatures11
.
In the shallow crust, magma degassing can also cause strong fractionation of D/H but
should produce a positive correlation with H2O due to the affinity of D for the vapor
phase25
. Positive trends are not, however, observed in the data, and we conclude that
degassing before entrapment did not play a significant role in modifying δD values of the
Cascade or Marianas samples.
Initial δD values (corrected as described above) from the Cascade melt inclusions
fall in a range from -95 to -70‰, despite a large range in H2O (Fig. 2.3a). These values
are isotopically lighter than those for the Marianas, which range from -55 to -12‰11
(Fig.
2.3a). Marianas melt inclusions have δD values that are higher than mantle values
(-80±10 ‰)26
, and have been interpreted to result from addition of D-enriched fluids to a
relatively D-depleted mantle wedge11
. Other estimates of δD for arc magmas based on
phenocrysts (-47 to -25‰ for Kamchatka)27
and fumarolic gases (-30 ± 10‰ for arcs
globally)28
agree well with the Marianas melt inclusion values. Although the Cascade
values overlap with mantle values, a minimum of 67–79% of the H2O in the Cascade
magmas must be sourced from a hydrous subduction component (Fig. 2.2a). We interpret
15
the lighter isotopic values for the Cascades to represent fluids sourced from a plate that
has experienced more dehydration prior to reaching sub-arc depths than in the Marianas.
As the slab becomes progressively more dehydrated, it becomes isotopically lighter as D-
enriched fluids are removed. Thus, fluids released at higher temperatures and greater
extents of slab dehydration should have more negative δD values than fluids that were
removed from the slab at lower temperatures. An alternative possibility is that the
differences in δD between the Cascades and other arcs is the result of large-scale
diffusive fractionation of D and H in the slab, mantle and/or crust during migration of
fluids and melts. Although this cannot be ruled out, it would require that the transport of
H2O is largely diffusive rather than advective, which is inconsistent with field evidence
for fluid migration through fracture networks (see Supplementary Information A.).
2.4. D/H Fractionation Model
To test the interpretation that differences in δD between the Cascades and
Marianas are due to different extents of slab dehydration, we created a model that
describes D/H fractionation during dehydration reactions in the subducted plate beneath
the two arcs. Using an equilibrium fractionation equation (Supplementary Eq. 1), we
calculated the δD of fluids progressively released from the slab with increasing
temperature and depth. We calculate H2O released from the slab by coupling a 2-D
thermal model2 with the thermodynamic calculation code Perple_X
29,30. We divide the
slab into 1000-m wide vertical columns and calculate the cumulative δD value of fluid
16
released from each column from the shallowest to the deepest column, assuming that the
slab consists of 2 km of basalt, 5 km of gabbro, and 2-4 km of hydrated mantle peridotite
(Fig. 2.3b, 2.3c; see Supplementary Fig. A.4 and Information), using temperature and
lithologically dependent fractionation factors (Supplementary Fig. A.5). A sedimentary
package was excluded from this model because most clay minerals break down at
shallow depths (5-10 km; ~250-450C) and contribute little to the fluid flux at sub-arc
depths6,21
.
Model results show that beneath the southern Cascades, the upper portions of the
slab, consisting of MORB volcanics and lower crustal gabbros, become completely
dehydrated by ~65 km depth (Fig. 2.3b), similar to previous predictions6. The hydrated
upper mantle portion of the subducted plate is able to carry bound H2O to greater depths
in the form of chlorite, but this phase is predicted to break down when the slab top
reaches ~80-90 km depth, which is directly beneath the volcanic arc (Fig. 2.3b). Our
model predicts two fluid pulses from the subducted plate: one beneath the forearc from
final dehydration of MORB volcanics and gabbros in the crustal part of the slab and
another beneath the arc from chlorite breakdown in the upper mantle portion of the slab.
The predicted depths of these fluid pulses correlate well with regions of low electrical
resistivity and low shear wave velocity in the overlying mantle wedge as imaged by
magnetotelluric and seismic data, respectively31,32
.
17
Figure 2.3. Hydrogen isotopes: measured values and model results. a) H2O versus δD
for Lassen (green shaded region excludes inclusions severely affected by H-loss; colored
symbols are initial values; errors based on diffusion correction; Table 2.1; Supplementary
Information A.), the Marianas Arc11
, Koolau48
, Manus Basin49
, MORB26
and arc
fumaroles28
. b) Distribution of bound H2O in the slab calculated with our Lassen thermal
model (Supplementary Fig. A.4 and Information). Slab thickness exaggerated x3. c)
Fractionation model results. δD of fluids released from the entire slab package as a
function of slab top depth beneath the Cascades (green) and Marianas (blue). Uncertainty
is ±15‰ (shaded regions; 2σ; Supplementary Fig. A.4 and Information). Grey boxes
show range in melt inclusion data at sub-arc depths.
18
At sub-arc depths beneath the Lassen region, modeled values of δD of the
hydrous component released from the slab overlap with corrected melt inclusion values
(Fig. 2.3b, 2.3c). This agreement suggests that Cascade arc magmas record the D/H ratio
of fluids derived from the deeper interior of the slab. The δD values of antigorite- and
chlorite-bearing peridotites, interpreted as subducted slab mantle, from Cerro del Almirez
(Spain)33
agree well with our model predictions (see Supplementary Information A.). In
contrast to the Cascades, model results for the Marianas (Fig. 2.3c), where older oceanic
crust is being subducted, show that temperatures within the slab remain cool enough to
carry bound H2O in hydrated upper mantle well past sub-arc depths (~160 km). In the
Marianas, modeled D/H values for fluids released from the plate overlap with the lowest
measured melt inclusion values. Although the modeled values do not reproduce the full
range of the data for the Marianas, the model does predict higher δD values for fluids
released beneath the Marianas arc compared to the Cascades.
2.5. Evidence and Implications for Slab Melting
Beneath the Lassen region, the upper, completely dehydrated portions of the plate
are likely at or above the MORB + H2O21
and sediment + H2O22
solidi (Fig. 2.2b). Our
model results predict that H2O-rich fluids are released from the slab interior during
chlorite breakdown at sub-arc depths, providing H2O that could cause partial melting of
the slab top. Although sediment melting imparts a distinctive trace element signature on
many arc magmas worldwide34
, in the Lassen Region it appears to be subordinate to
contributions from the subducted basaltic crust13
. Previous work in the Lassen
segment13,14
found that magmas with the highest (Sr/P)N, and therefore the greatest
19
amount of subduction component, have the lowest Sr isotope ratio (87
Sr/86
Sr = 0.7029-
0.7034), similar to unaltered Gorda Ridge MORB35
(87
Sr/86
Sr = 0.7024; Supplementary
Fig. A.6). In light of our new results, we interpret the MORB-like 87
Sr/86
Sr signature to
reflect hydrous partial melting of Gorda MORB in which altered domains with radiogenic
Sr derived from seawater have lost much of their Sr during the shallower stages of
dehydration (see Supplementary Information A.). Strong negative correlation of 87
Sr/86
Sr
and (Sr/P)N in the Mt. Shasta region15
is also consistent with this interpretation, but
existing data for other segments of the arc further to the north do not show this pattern36,37
(Supplementary Fig. A.6).
Our results provide a mechanism for melting of sediments and basalt in the upper
part of the subducted oceanic plate by fluids rising from deeper parts of the slab17,38,39,40
.
Because melting of the upper oceanic crust takes place in the garnet stability field, a
hallmark of slab melting is the geochemical signature imposed by garnet, such as high
Sr/Y and La/Yb. Lavas from the Cascades and other relatively hot-slab subduction zones
like Mexico have values of these ratios that are higher than most other arc magmas, but
not as extreme as many so-called adakites, which are interpreted to be slab melts41
. Wet
melts of the basaltic crust are expected to be andesitic to dacitic in composition42,43
and
will infiltrate and react with the overlying mantle wedge and lower its solidus
temperature as they rise from the plate interface. A comparison of temperature sensitive
(H2O/Ce) and garnet sensitive (La/Yb) parameters for arc magmas worldwide
(Supplementary Fig. A.7) lends support to our interpretation that slab melting plays an
increasingly important role in arcs where younger, warmer oceanic crust is being
subducted.
20
2.6. Bridge
In the preceding chapter (II), the hydrogen isotopes compositions of olivine-
hosted melt inclusions from seven cinder cones in the Lassen region were compared with
a thermo-petrologic model to investigate slab dehydration and melting beneath the
Cascade Arc. The next chapter (III) uses the volatile contents, major and trace elements,
and the B isotope compositions of olivine-hosted melt inclusions from eight cinder cones
(one in addition to the seven discusses in chapter II) to provide further evidence for the
conclusions drawn in chapter II and investigate magma generation processes in the
mantle wedge beneath the southern Cascades.
21
CHAPTER III
SLAB MELTING AND MAGMA FORMATION BENEATH THE
SOUTHERN CASCADE ARC
This chapter includes material co-authored with Dr. P.J. Wallace, Dr. M.A.
Clynne, Dr. D. Weis, and Dan Rasmussen. Sample collection was performed by me with
the help of Dr. Wallace and Dr. Clynne. All melt inclusions were prepared and analyzed
by me using Fourier transform infrared spectroscopy (H2O and CO2), electron
microprobe (major elements), laser ablation inductively coupled plasma mass
Spectrometry (trace elements), and secondary ion mass spectrometry (B isotopes), with
assistance from D. Rasmussen for two cinder cones. Analyses, data corrections,
geochemical modeling, and interpretation were performed by me, with the help of Dr.
Wallace. Radiogenic isotopic analyses on bulk tephra were performed by Dr. Weis.
Models of mantle melting, using pMELTS, were performed by me. I drafted all the
figures used in this article and the text was written by me, with editorial assistance by Dr.
Wallace.
3.1. Introduction
Dehydration of subducted oceanic lithosphere drives arc magmatism at
convergent plate margins. However, the thermal structure of an individual subduction
zone controls the depths at which key dehydration reactions occur (Schmidt and Poli,
1998; Hacker et al., 2008; Van Keken et al., 2011; Wada et al., 2012), and consequently,
affects the composition and sources of fluids and/or melts (e.g., Cooper et al., 2012;
22
Ruscitto et al, 2012) that infiltrate the mantle wedge to trigger melting. The thermal
structure is commonly assessed using the thermal parameter (Φ), which is a function of
downgoing plate age, dip angle, and convergence rate (Syracuse et al., 2010, Wada and
Wang, 2009). Variability in Φ globally is predicted to cause a wide range of slab surface
temperatures beneath arcs (give T range), as estimated from geodynamic models
(Syracuse et al, 2010; Wada and Wang, 2009) and geochemical tools (Plank et al., 2009;
Cooper et al., 2012). The results suggest a continuum of subduction zones between ‘cold’
(i.e., Tonga, Kamchatka) and ‘warm’ slabs (i.e., the Cascades, Mexico). Although fluids
released from the subducting slab have been shown to become more solute-rich with
increased temperature (Manning, 2004; Kessel et al., 2005a; Herman and Spandler, 2008;
Cooper et al, 2012; Ruscitto et al, 2012), whether or not the oceanic crust begins to melt
beneath arcs has been debated, despite geochemical evidence for slab melt contributions
beneath some warm-slab endmembers such Mexico (e.g., Cai et al., 2014), and the
Cascades (Walowski et al., 2015). Isolating the role of different components in the
subducted lithosphere (altered oceanic crust, sediments, serpentinized peridotite) and how
each component transfers material to the overlying mantle wedge (as fluids, melts or a
supercritical phase), is important for our understanding of mass transfer to the mantle,
both beneath and beyond arcs, as well as the processes by which the mantle melts in
subduction zones.
The Cascade arc represents a global warm-slab endmember due to slow shallow
subduction of young oceanic crust (6-10 Ma at the trench; Wilson et al., 2002; Kirby et
al., 2002). Estimations from geodynamic models (Syracuse et al., 2010; Wada and Wang,
2009) and geochemical studies (Cooper et al., 2012; Ruscitto et al., 2012; Walowski et
23
al., 2015) agree that slab surface temperatures beneath the arc axis are hotter, on average,
than many other arcs globally. Previous work in the central Cascades has suggested that
the mantle wedge beneath the arc receives a reduced flux of volatiles from the downgoing
slab (Ruscitto et al., 2012), and H2O concentrations in olivine-hosted melt inclusions
from both the central and southern Cascades (~3.2 wt%; Ruscitto et al., 2010, 2011,
LeVoyer et al., 2010) fall slightly below the global average (~3.9 wt%; Plank et al.,
2013). Walowski et al. (2015) found that hydrogen isotope ratios of primitive magmas
from the Lassen region of the southern Cascades are lighter than those for the Marianas.
This was demonstrated to reflect waning dehydration of the deep slab interior (hydrated
mantle) after the crustal portion of the slab had already dehydrated beneath the forearc.
These results also provide evidence that flux-melting of the oceanic crust occurs when
the fluids released from the slab interior interact with oceanic crust that is above its wet
solidus temperature (i.e., Skora and Blundy, 2010; Till et al., 2012; Spandler and Pirard,
2013).
We measured the volatile contents, major element, trace element, and B isotope
compositions of olivine-hosted melt inclusions and the radiogenic isotopic compositions
of bulk tephra from the same eruptive centers in the Lassen region that were studied by
Walowski et al. (2015) for H isotopes. With these near-primary mantle melts, we aim to
quantify the chemical contributions from the subducting oceanic lithosphere to better
understand how subduction of warm oceanic crust affects the composition of mantle
melts and the productivity of melting in the mantle wedge. Lastly, we test the hypothesis
presented by Walowski et al. (2015) that magma production beneath the southern
24
Cascade Arc involves a multi-stage process that includes flux melting of the subducted
oceanic crust and hydrous slab melt addition to the overlying mantle wedge.
3.2. Geologic Setting
The Lassen Segment is the southern terminus of the active Cascade arc (Guffanti
and Weaver, 1988). Volcanism is the result of oblique subduction of the Gorda micro-
plate beneath the North American plate (Fig. 3.1; Wilson, 2002), producing dominantly
calc-alkaline magmas (Clynne and Muffler, 2010). Westward expansion of the Basin and
Range extensional province into the eastern flanks of the Cascade Arc, including the Hat
Creek and Lake Almanor Grabens, has produced many normal faults that provide
pathways for mafic magmas to reach the surface (Guffanti et al., 1990; Clynne and
Muffler, 2010). The Quaternary volcanics in the Lassen region sit above a broad platform
of mafic to intermediate volcanoes and volcanic products 2-4 km thick (Berge and
Stauber, 1987). This volcanic platform is underlain by plutonic Sierran and metamorphic
Klamath terrain basement rocks as suggested by constant modeled seismic velocities
across the Sierra Nevada-Cascade Range boundary (Berge and Stauber, 1987).
Surrounding the volcanic center of Lassen Peak, a dacitic dome complex (Clynne
and Muffler, 2010), is a large volcanic field containing over 500 monogenetic cinder
cones and small shield volcanoes erupted in the last 12 Ma (Guffanti et al., 1990).
Previous work on these mafic cinder cones has identified a range in compositions from
low-K tholeiitic basalts to calc-alkaline basalts, basaltic andesites, and andesites (Clynne,
1993; Borg et al., 1997). Also observed in the most primitive calc-alkaline volcanic rocks
is distinct across-arc geochemical variability interpreted to be caused by variable
25
Figure 3.1. Sample locations and across-arc geochemical variability. a) Regional map of
the Northwestern United States showing major tectonic boundaries. The Cascade
volcanic arc is defined by the major peaked labeled with black triangles. Lassen Peak is
highlighted in red. Black arrows show direction and are labeled with the convergence rate
relative to North America (Wilson et al., 2002). b) Larger scale map of the Lassen region
with locations of vents sampled in this study (BRVB: Basalt of Round Valley Butte,
BPB: Basalt of Poison Butte, BRM: Basalt of Red Mountain, BBL: Basalt of Big Lake,
BAS-44: Basalt of Hwy 44, BPPC: Basalt of Paine Parasitic Cone, BORG: Basalt of Old
Railroad Grade, and CC: Cinder Cone; see Table 3.1 for details) and previously sampled
by Clynne (1993) and Borg (1995; grey diamonds). Lassen Peak (large white triangle),
outcropping basement rocks (shaded pink areas), major highways (thin black lines), and
large lakes (shaded blue regions), are also highlighted. c) Distance from the trench vs.
Sr/Nd and d) 87Sr/86Sr for samples in this study(colored symbols) and Borg et al. (1997;
grey diamonds). Symbols and colors for individual cinder cones are consistent throughout
the manuscript.
26
enrichment of the mantle by a subduction component, a key factor for targeting this
region in our study (Fig. 3.1; Borg 1997, 2002). Figure 3.1 shows variations in both
Sr/Nd and 87
Sr/86
Sr with increasing distance from the trench. Decreasing Sr/Nd has been
interpreted to indicate the waning addition of a subduction component towards the back-
arc (Borg et al., 1997). The 87
Sr/86
Sr compositions, however, increase toward the back-
arc, indicating that the subduction component has a less radiogenic Sr isotope signature
than the sub-arc mantle. Furthermore, variability in Nb/Zr suggests that the Lassen sub-
arc mantle is heterogeneous (Borg et al., 1997; Walowski et al., 2015), but there are no
systematic variations of Nb/Zr with distance from the trench.
3.3. Sample Descriptions and Analytical Methods
Samples were collected from the tephra deposits of Quaternary monogenetic vents
spanning ~80 km from the forearc to the backarc (Fig. 3.1). Vents that erupted primitive
basalt or basaltic andesite (MgO > 7 wt%) identified from bulk rock analyses (Clynne,
1993; Borg et al., 1997) were targeted because they are close to primary mantle melts in
composition. Coarse ash was collected because it quenches more rapidly than lava,
bombs, and lapilli, minimizing the potential for syn-eruptive diffusive H loss or
crystallization of melt inclusions (e.g., Lloyd, 2013). Loose olivine crystals (50 μm to 1
mm in size) were hand-picked from washed and sieved tephra. The olivine crystals were
treated in HBF4 to remove glass adhering to the crystal surface and examined in
immersion oil (refractive index 1.675) to locate melt inclusions. Olivine crystals hosting
fully enclosed, glassy melt inclusions were mounted in acetone-soluble resin on glass
slides and prepared as doubly polished wafers. H2O and CO2 concentrations of the melt
27
inclusions were measured at the University of Oregon using a Thermo-Nicolet Nexus 670
FTIR spectrometer interfaced with a Continuum IR microscope. Concentrations were
calculated from IR peak absorbances using the Beer–Lambert law and compositionally
appropriate absorption coefficients (see Johnson et al., 2008, for details). Melt inclusions
and host olivine were analyzed for major elements (plus S and Cl for inclusions) on the
Cameca SX-100 electron microprobe at the University of Oregon (see Ruscitto et al.,
2010, for details). Melt inclusions were subsequently analyzed for a suite of trace
elements on the Photon Machines Analyte G2 193 nm ArF ‘‘fast’’Excimer Laser system
at Oregon State University, using 50 µm spot size with a 5 Hz pulse rate. Measured trace
element concentrations were determined by reference to GSE-1G glass as a calibration
standard and using 43
Ca as an internal standard (see Loewen and Kent, 2012, for details).
BHVO-2G, BCR-2G, and GSD-1G glasses were also analyzed to monitor accuracy and
precision, and the analyzed values were within 10% of accepted values.
A subset of the melt inclusions that were analyzed for H isotopes and trace
elements by Walowski et al. (2015) were also analyzed for B isotope ratios using the
Cameca IMS 1280 at the Northeastern National Ion Microprobe Facility, Woods Hole
Oceanographic Institution, with O- primary beam, 20-40 nA primary current, 10,000 V
secondary voltage, and a 10 µm spot size. More detailed methods are described in
Marschall and Monteleone (2014). Some of the melt inclusions were too small to allow a
new SIMS spot adjacent to an existing NanoSIMS spot (20x20 rastered area, ~5 µm
deep). In these cases, the SIMS spot was placed within the pre-existing NanoSIMS spot.
Tests comparing measurements within pre-existing spots to those on a clean surface from
a single melt inclusion revealed no systematic differences.
28
Sr, Nd, Hf, and Pb isotope ratios were measured at the Pacific Centre for Isotopic
and Geochemical Research at the University of British Columbia. Pb, Nd, and Hf isotope
ratios were measured by MC-ICP-MS (Nu Instruments Ltd., Nu II 214), and Sr isotope
ratios were measured by Thermo Finnigan Triton TIMS using procedures described in
Weis et al. (2007) and Weis et al. (2006). Additional details regarding sample preparation
and analytical techniques are given by Mullen and Weis (2015). Tephra from sample CC
was excluded from isotopic analyses due to clear crustal contamination (abundant quartz
xenocrysts) of the bulk material.
3.4. Results
3.4.1. Melt Inclusion Major and Trace Element Compositions
The olivine host crystals vary from Fo84 to Fo90 (Table 3.1). For each cinder cone,
11-17 melt inclusions were analyzed and individually corrected for post-entrapment
crystallization (PEC) and Fe-loss using Petrolog 3.1 (Danyushevsky and Plechov, 2011;
Danyushevsky, 2000). Volatile contents and trace elements, which are not included in the
Petrolog calculations, were also corrected using the ratios of K2O in corrected and
uncorrected inclusions. Initial Fe contents were based on the FeOT of the bulk tephra or
individual melt inclusions with the highest MgO and FeOT at a single cone (bulk tephra
compositions were not available for cones BBL and CC). Calculated percentages of PEC
for all melt inclusions range from 0 - 14%. Corrected melt inclusion
compositions overlap with the most primitive lava samples previously analyzed in the
Lassen region (Fig. 3.2) and contain MgO concentrations of 7.4 - 9.8 wt%
29
Table 3.1. Averaged Primary Melt Compositions.
30
Figure 3.2. Corrected melt inclusion major and trace element compositions. a) Average
melt inclusion trace element composition for each vent normalized to normal-MORB (N-
MORB; Sun and McDonough, 1989) and compared with previously determined end-
member compositions (CAB, Borg et al. 1997; HAOT, Bacon et al. 1997). b) K2O and
SiO2 contents of individual melt inclusions (corrected, volatile-free normalized values)
compared with bulk rock analyses from Clynne, (1993; grey diamonds). Classification of
low-, med-, and high-K based on Peccerillo and Taylor (1976).
(Supplementary Table B.1; see Apendix B for all supplementary information for this
chapter). To estimate a primary melt composition for each cone, we incrementally added
equilibrium olivine (0.1 wt% steps) to the average melt inclusion composition from each
cone until the melt composition was in equilibrium with mantle olivine (Fo90; Table 3.1;
31
Ruscitto et al., 2010). The calculated primary melt compositions required addition of 1-
20% equilibrium olivine (Table 3.1).
The melt inclusion glasses are dominantly medium-K calc-alkaline basalt (CAB),
with some that fall into the low-K field (Fig. 3.2a). Previous work in the Lassen region
has suggested that low-K tholeiitic magmas (also called high-alumina olivine tholeiites;
HAOT) and calc-alkaline magmas have fundamentally different source regions (Clynne,
1993; Bacon et al., 1997; Baker et al., 1994). However, the low-K samples used in this
study do not display the lower LREE/HREE and LILE/HFSE values typical of the
endmember HAOT volcanic rocks in this region (Fig. 3.2, Bacon et al., 1997). Rather, all
compositions used in this study display similar trace element patterns to the regional
CABs (Fig. 3.2), suggesting that despite variability in major and trace element
compositions, they likely formed as the result of flux-melting, and not decompression
melting of the mantle.
3.4.2. Magmatic Volatile Contents
Dissolved H2O contents of the melt inclusions range from 0.6-3.5 wt%. At
individual cinder cones, a range in H2O concentrations is observed and is likely due to
differences in extent of pre-entrapment degassing (Metrich and Wallace 2008; Johnson et
al., 2009) and post-entrapment hydrogen loss (Lloyd et al., 2013, Gaetani et al., 2012,
Bucholz et al., 2013). Because these processes systematically decrease H2O
concentrations, the maximum measured H2O/K2O ratio for each cone was used to
estimate the initial H2O content (H2Omax) of the magma erupted at that cone. In the
Lassen region, H2Omax ranges from 1.3-3.4 wt%. Primary melt H2O concentrations (1.1-
32
3.4 wt%, calculated from H2Omax using the olivine addition method described above;
Table 3.1) overlap with calculated primary melt H2O values for basaltic and basaltic
andesite melt inclusions from central Oregon (1.4-3.0 wt%; Ruscitto et al., 2010). In
contrast to H2O, Cl is not affected by degassing and post-entrapment diffusive effects.
Concentrations of Cl in calculated primary melts range from 100-600 ppm, except at
BRM, where Cl values are as high as 2500 ppm (Supplementary Table B1).
3.4.3. Isotopic Compositions
The δ11B values from individual cinder cones in the Lassen region range from
-9.9‰ to -2.4‰ (Table 3.1; Fig. 3.3). These values overlap with those measured for bulk
rock samples from the southern Washington Cascades, which range from -9‰ to -0.4‰
(Leeman et al., 2004), and those from melt inclusions from Mt. Shasta (Fig. 3.3; Rose et
al., 2001; LeVoyer et al., 2010). Melt inclusions from the Cascades have lower B
concentrations and more negative δ11B than those measured in other arcs, such as
Kamchatka and Japan, where older oceanic crust subducts (Fig. 3.3; Ishikawa et al.,
2001; Ishikawa and Tera, 1999).
The Sr, Nd, Hf, and Pb isotope measurements for bulk tephra samples overlap
with those previously determined for volcanic rocks in the Lassen Region (Borg et al.,
1997; Borg et al., 2002) and show variability in 87
Sr/86
Sr (0.703396-0.703985±0.000007),
208Pb/
204Pb(38.4640-38.6503±0.0026),
177Hf/
176Hf (0.283035-0.283094±0.000006), and
143Nd/
144Nd (0.512827-0.512948±0.000006) (Table 3.1).
33
Figure 3.3. Boron isotope compositions. Each data point (symbols as in Fig. 3.1)
represents an average from 4-6 individual melt inclusion analyses. Data for comparison
from the southern Washington Cascades (Leeman et al., 2004; filled squares, whole rock
analyses) Mt. Shasta (Rose et al., 2001, open circles; individual melt inclusions; LeVoyer
et al., 2010, filled circles), the Marianas (Ishikawa, 2001), and Kamchatka (Ishikawa and
Tera, 1999). Dashed black curve represent mixing between MORB (Chaussidon and
Jambon, 1993) and a hydrous slab fluid (Marschall, 2007).
3.5. Discussion
3.5.1. The Source of Volatiles in Lassen Region Primitive Magmas
B is a highly fluid mobile element, and because it is found in higher
concentrations in subducted materials than the mantle, it can be an excellent tracer of
fluids derived from subducting slabs (e.g., Bebout et a.,1993, Ryan and Langmuir 1993,
Tonarini et al., 2001). In addition, subducted materials such as sediment, oceanic crust,
and serpentinitized mantle have δ11B signatures that are distinct from the mantle wedge
(e.g., Ishikawa and Nakamura, 1993; Smith et al., 1995; Boschi et al., 2008; Chaussidon
and Jambon, 1994). However, the B isotopic composition and low B concentrations in the
34
melt inclusions from the Lassen region suggest that the sub-arc mantle receives little to
no B from the subducting slab (Fig. 3.3). This is probably the result of extensive
dehydration of the slab before it reaches sub-arc depths (Leeman et al., 2004; Manea et
al., 2014). Geodynamic modeling and calculated metamorphic phase equilibria suggest
that H2O can be carried to sub-arc depths by the hydrated mantle portion of the
downgoing slab, in the form of chlorite, beneath the Lassen region (van Keken et al.,
2011; Walowski et al., 2015). The D/H ratios measured in melt inclusions from the
Lassen region are in agreement with modeled values which indicate that fluids are likely
sourced from the final breakdown of chlorite in the deep slab interior (Walowski et al.,
2015). Because nearly all B is released from hydrated peridotite during the antigorite
breakdown reaction (which occurs in the slab beneath the Cascades before reaching sub-
arc depths), chlorite-derived fluids contribute little to no B to the subduction component
(Spandler et al., 2014). This explains how the slab beneath the Cascades can release a
hydrous slab component to the mantle wedge that contains very little B, such that
primitive magmas formed in the wedge have B isotope ratios and concentrations typical
of mantle-derived magmas (MORB).
Despite low B concentrations, H2O and Cl are high compared to MORB, which
requires that these volatiles are retained in the slab to greater depths than B (Spandler et
al., 2014). Furthermore, strong correlations of H2Omax/Ce and Cl/Nb with Sr/Nd clearly
demonstrate that volatile and trace element enrichments are coupled and therefore are
derived from the same process (Fig. 3.4). To better quantify this relationship, we
calculated partial melt compositions for two mantle endmembers to which variable
amounts of subduction component were added. Figure 3.4 shows good agreement
35
between the model curves and the melt inclusion data, which indicates that volatile and
trace element variability at different cones is the result of different amounts of a
subduction component added to a heterogeneous mantle wedge. However, in some cases,
such as BRM, a sample will have a lower H2O/Ce for a given value of Sr/Nd than
predicted by the melting model. This may be caused by variability in the H2O and trace
element ratios of the hydrous subduction component, or it may suggest that at some
cones, H2Omax is still a partly degassed composition (either because of pre-entrapment
degassing or post-entrapment H loss). Cl/Nb should provide a more robust indication of
initial volatile concentration because Cl is not affected by diffusive loss and only
degasses at very low pressure. Good agreement between the data and melting models for
Cl/Nb vs. Sr/Nd provides support for the interpretation that initial H2O concentrations are
related to the amount of a subduction component added to the mantle wedge beneath the
arc and that the slab component has ratios of H2O and Cl to LILE that are not highly
variable (Fig. 3.4b and c). This evidence indicates that BRM, the sample with the highest
Sr/Nd and therefore largest amount of a subduction component, has very low H2O/Ce as
the result of extensive degassing in the crust or post-entrapment hydrogen diffusive loss.
Volatile and trace element ratios from the central Oregon Cascades can also be
explained using the calculated melting curves, but require subduction component addition
to a more enriched mantle source than most Lassen region magmas (Fig. 3.4a; Ruscitto et
al., 2010). Interestingly, melt inclusions with the highest values of Sr/Nd in both the
Lassen region (BRM) and the Mt. Shasta region do not have the highest values of
H2O/Ce, but they do have the highest Cl/Nb, and also have Cl concentrations
significantly higher than other cones throughout the Cascades. As suggested above, these
36
magmas likely experienced extensive degassing of H2O in the crust before melt inclusion
entrapment, and/or were affected by post-entrapment H loss. However, if the BRM and
Mt. Shasta magmas had pre-degassing compositions that fit the model curves in Figure
3.4a, they would have initially had up to ~8-10 wt% H2O. This is consistent with
experimental phase equilibria showing that high-Mg basaltic andesites and andesites at
Mt. Shasta had very high initial H2O contents (10-14 wt%; Krawczynski et al., 2012).
Such high initial H2O is also consistent with the very high Cl/Nb values for high-Mg
basalts and basaltic andesites at Mt. Shasta (Ruscitto et al., 2011).
Figure 3.4. Corrected melt inclusion volatile and trace element ratios. a) H2O/Ce vs.
Sr/Nd (corrected melt inclusions that contain H2O concentrations within 0.5 wt% of the
H2Omax from each cone to represent the least degassed compositions), b) Cl/Nb vs. Sr/Nd
(all melt inclusions; corrected) and c) Cl/Nb vs. Sr/Nd (y-axis extents to higher values,
average values calculated using corrected melt inclusions from each cone). Data from
central Oregon (Ruscitto et al., 2010; restored melt inclusions; solid blue circles enclosed
in light blue shaded field) and Mt. Shasta (Ruscitto et al., 2008; restored melt inclusions;
primitive basaltic andesite (PBA): solid grey triangles enclosed in grey shaded field;
high-Mg andesites (HMA): open grey triangles enclosed in a grey shaded field), for
comparison. Black lines represent 10% partial melts of two endmember mantle
compositions (DMM; Workman and Hart, 2005; average central Oregon mantle; Ruscitto
et al., 2010) mixed with variable amounts of a hydrous subduction component (grey
diamond; calculated using methods of Portnyagin et al. (2007), with primary mantle
composition of BORG; Table 3.1). Grey bar represents the range in sub-arc mantle
compositions determined by Walowski et al. (2015). Melt inclusions that have
experienced degassing or syn-eruptive H loss will cause deviation from the melting
curves as indicated by the black arrow in panel (a).
37
The Blanco Fracture zone, which separates the Juan de Fuca and Gorda plates,
may provide a pathway for deep serpentinization of the upper mantle in the downgoing
slab offshore of the Cascades, and has been proposed to source the volatile-rich
component at Mt. Shasta (Grove et al., 2002; Manea et al., 2014) However, plate
reconstructions and symmetry of the fracture zone on the Pacific plate suggest that the
Blanco Fracture zone is not old enough to project beneath the arc (Wilson, 2002), and
thus, the causes of the geochemical differences between the Mt. Shasta and Lassen
regions (Fig. 3.4) remain enigmatic.
3.5.2. Evidence for Slab Melting
Previous work using trace elements and radiogenic isotopes in the Lassen region
found negative correlations between LILE/LREE ratios and 87
Sr/86
Sr, which suggests that
the subduction component is less radiogenic than the sub-arc mantle (Borg et al., 1997,
2002). New radiogenic isotope data from this study overlap with the published data (Fig.
3.5). Because elevated H2O/Ce, Cl/Nb, and Sr/Nd ratios are related to subduction
component addition, our data confirm that the subduction component is MORB-like, with
less radiogenic Sr and Pb isotopic composition and more radiogenic Nd isotope
composition than the Lassen region sub-arc mantle. In its isotopic characteristics, the
subduction component beneath the Lassen region is similar to offshore Gorda Ridge
MORB (Davis et al., 2008). However, a major contribution from the melting of
subducted MORB crust was originally discounted because dry eclogitized oceanic
lithosphere requires higher temperatures than expected for the slab top at sub-arc depths
(Borg et al., 1997). Similar isotopic and trace element relationships are observed in the
38
Mt. Shasta region (Fig. 3.5). Grove et al. (2002) discounted slab melting beneath Shasta
as a possible explanation because models of hydrous peridotite melting could reproduce
the observed major element compositions of primitive volcanic rocks in that region.
Recent work by Walowski et al. (2015) interpreted the light D/H values of melt
inclusions from the Lassen region as resulting from final dehydration of chlorite in the
hydrated upper mantle portion of the downgoing slab. This provides a mechanism to
deliver H2O to the MORB-volcanic portion of the slab top and drive wet slab melting
beneath the arc.
To further test this hypothesis, we calculated mixing and partial melting models
involving the Lassen sub-arc mantle and a partial melt of Gorda Ridge MORB (Fig. 3.5).
Because temperatures of the plate top are at or above the wet MORB and wet sediment
solidi (Schmidt and Poli, 1998; Herman and Spandler, 2008), we assume the subduction
components are partial melts rather than aqueous fluids (Cooper et al., 2012; Ruscitto et
al., 2012; Walowski et al., 2015). We also assume that the Gorda MORB component is
unaltered. This assumption relies on the fact that oceanic crust is heterogeneously altered
during hydrothermal alteration (e.g., Bach, 2003), and that the unaltered portions retain
their MORB-like signature, whereas altered zones likely lose most of their seawater-
enriched Sr beneath the forearc during transition to ecologite (Walowski et al., 2015).
Because Sr/Nd is an indicator of subduction enrichment, primitive basalts and basaltic
andesite with the lowest Sr/Nd values should be most representative of the Lassen sub-
arc mantle. For the samples with the lowest Sr/Nd, a small range of Sr, Nd, and Pb
isotope ratios are observed, and these ranges are probably indicative of mantle
heterogeneity beneath the arc, as previous suggested by Borg et al. (1997; 2002) and
39
Figure 3.5. Radiogenic isotope compositions and slab melt mixing models. a) Bulk
tephra compositions of a) 87
Sr/86
Sr b) 208
Pb/ 204
Pb, and c) 143
Nd/144
Nd vs. average Sr/Nd
from melt inclusions for each cone (symbols as in Figure 3.4). Isotopic composition of
BRM is from Borg et al. (1997), as it was not analyzed in this study. CC was omitted due
to evidence for crustal contamination (see main text). Bulk lava analyses from the Lassen
Region and M. Shasta (Borg et al., 1997; Grove et al., 2002, respectively) for
comparison. North Cascade sediment (yellow shaded region; Carpentier et al., 2013,
2014) and northern Sierran granites (grey shaded region; Cecil et al., 2012) highlighted to
show possible components that may contribute to trace element and radiogenic isotope
variability of samples. Melting models (dashed lines) calculated using the batch melting
equation for a range in mantle sources (calculated for the Lassen sub-arc mantle; see text)
mixed with 2, 5, and 10% (labeled on modeled curves) of a 5% partial melt of Gorda
MORB (Davis et al., 2008; partition coefficients from Kessel et al., 2005a; at 4 GPa,
1000C). Bulk partition coefficients calculated for a spinel peridotite assemblage
35/30/12/5-Ol/OPX/CPX/Sp (Hughes and Taylor, 1986) using mineral partition
coefficients of Eiler et al. (2005) for Sr and Nd. Melt fractions derived from PMELTS
model results (for a given temperature and amount of slab melt addition; Fig. 3.6). d)
Lassen sub-arc mantle (based on bulk rock sample with smallest amount of apparent
subduction component) mixed with sediment partial melts (5%, large filled grey
diamond, and 20%, large filled grey diamond, melts of N. Cascade sediment using
partition coefficients from Kessel et al. (2005) a) and slab partial melts 5%, large filled
black diamond, and 20%, large filled black diamond, melts of Gorda MORB using
partition coefficients from Kessel et al. (2005a).
40
Clynne and Borg (1997). We thus use a range in sub-arc mantle compositions (Fig. 3.5;
87Sr/
/86Sr = 0.7039 - 0.7043,
208 Pb/
204Pb = 38.512 - 38.782 , and
143 Nd/
144Nd = 0.5127-
0.5128). Figure 3.5 shows curves that represent mantle melts formed by melting of the
sub-arc mantle mixed with variable amounts of Gorda MORB melt. The model results
suggests 1-10 wt% addition of a subduction component that is a slab melt. Although the
model results can explain a majority of the compositions, they under-predict some values
of Sr and Pb isotopes, and overpredict the range in Nd isotopes. There are three potential
explanations for these small offsets: 1) zones of alteration in the MORB volcanic section
of the downgoing plate that retained their isotopic signature even after complete
dehydration beneath the forearc, 2) involvement of small proportions of a sediment melt
component, and/or 3) contamination by continental crust. All three components may play
a role in causing the slight offset of the slab melt models from the Lassen data seen in
Figure 3.5. The latter two explanations will be discussed in further detail in the following
section.
Our proposed mechanism for slab melting relies on breakdown of chlorite in the
mantle portion of the downgoing oceanic plate. However, in the model shown in Figure
3.5, this component has been neglected in our melting calculations. Fluids produced from
the breakdown of chlorite at sub-arc depths have some distinct trace element
characteristics (e.g., elevated LREE/HREE), but overall, are solute poor (Spandler et al.,
2014), and as a result, will have little effect on the trace element composition of the
resulting magmas formed by flux melting of the upper oceanic crust. For example, Sr
concentrations in fluids produced from the breakdown of serpentine and chlorite range
from 1.7-2.8 ppm (Spandler et al., 2014), an insignificant contribution when compared to
41
the average Sr composition of oceanic crust, 90 ppm (Sun and McDonough, 1989). We
therefore conclude that fluids derived from chlorite breakdown in the hydrated mantle
portion of the slab dominantly contribute H2O to the system but do not impart a
distinctive trace element signature.
3.5.3. The Role of Sediment Melts and Crustal Assimilation
Low Sr/Nd magmas in the Lassen region have elevated 207
Pb/ 204
Pb, which was
previously used to suggest the sub-arc mantle was enriched by a sediment component, but
it was concluded that this took place during an earlier, possibly Mesozoic, subduction
event because young Pacific sediments did not have high enough Pb isotope ratios to
explain the values (Borg et al., 1997). However, radiogenic isotope ratios measured in
sediments offshore of Vancouver Island (Carpentier, 2014; Mullen and Weis, 2015) do
have high enough Pb isotopic ratios to explain the isotopic compositions of low Sr/Nd
magmas in the Lassen region. This new data allows for an alternative hypothesis that
variable proportions of hydrous melts of subducted oceanic crust and sediment make up
the subduction component in the forearc, whereas sediment melts dominate in the back-
arc. This hypothesis, however, requires bulk sediment addition to the mantle wedge
rather than sediment melting (Fig. 3.5). Because sediment melts are more physically
plausible given the relatively high slab top temperatures beneath the arc, this component
should display higher Sr/Nd than bulk sediment, similar to MORB partial melts, but does
not (Fig. 3.5). Furthermore, because thermo-petrologic models suggest that the slab
becomes completely dehydrated at sub-arc depths, this would require in-situ breakdown
of phengite at great depths to drive sediment melting behind the arc-axis (Spandler and
42
Pirard, 2013). However, low-velocity anomalies agree well with release of fluids from
final chlorite breakdown in the mantle portion of the slab at 80 km, and no further
evidence provides support for contributions from the slab past this depth. These
observations taken together suggest that subduction of a modern sediment component is
not responsible for the isotopic compositions of low-Sr/Nd magmas in the Lassen region
(Fig. 3.5).
Conversely, a modern sediment component may contribute to variability in
isotopic compositions of high-Sr/Nd magmas that trend to slightly more radiogenic
values of Sr and Pb, and less radiogenic values of Nd than predicted by the melting
model in Figure 3.5. To further distinguish between sediment and slab melt contributions,
we use Th/La systematics as a discriminant because of the high Th concentrations found
in sediments relative to MORB and sub-arc mantle (Fig. 3.6; Plank et al., 2005). The
mixing model in Figure 3.5d shows that Th/La variations in primitive Lassen region
magmas may result from addition of <5% of a subduction component that is made up of
variable proportions of sediment and MORB melts. At all but two cinder cones, melt
inclusion values suggest that <30% sediment melt contributes to the trace element and
isotopic enrichments.
Two cinder cones (BPB and CC) have larger apparent contributions from
sediment melts. Cinder Cone in particular contains the highest Th/La values from our
dataset. However, the bulk lava and tephra at this cone contain abundant quartz
xenocrysts and variably melted granitic xenoliths, which are clear indications of large
amounts of crustal contamination (M. Clynne, unpublished data). This sample was
therefore excluded from radiogenic isotope analyses. We also note that in general, melt
43
inclusions from the Lassen region samples have lower Th/La values on average than
many of the published bulk rock analyses from this area (Fig. 3.5; Borg et al., 1997,
2002). This may be because melt inclusions are trapped at depth, before even minor
crustal contamination occurs in the shallow crust prior to eruption. Previous work in the
Lassen region interpreted unradiogenic Pb and Os isotopic compositions in the relatively
primitive basalts and basaltic andesites as evidence for minimal contamination by
continental crust (Borg et al., 1997, 2000). However, because of very high Th
concentrations in the granitic basement rocks (Cecil et al., 2012), small amounts of
crustal addition could increase the Th/La ratio enough to make it difficult to differentiate
between sediment melt contribution and that of the basement rocks.
3.5.4. Modeling Slab Melt Addition to the Mantle Wedge
To determine the influence of slab melt addition to the mantle wedge, we used
pMELTS (Ghiorso et al., 2002) to compare the effects of fluid addition and hydrous melt
addition to the mantle wedge at temperatures and pressures expected for the Lassen sub-
arc mantle. To do this, we created a mantle-wedge source composition by adding various
amounts of either a dacitic slab melt (Klimm et al., 2008) or pure H2O to a primitive
mantle composition (MM3; Baker and Stolper, 1994). The pMELTS program was then
used to determine the phase equilibria of the bulk mixture from 900-1400 C at a pressure
of 1.5 GPa. These values are based on temperatures from geodynamic model results for
the Lassen region (Walowski et al., 2015), beginning at the slab-wedge interface to
~100°C hotter than peak temperatures expected in the mantle wedge. Although this
method does not attempt to model the kind of reactive transport mechanism that likely
44
occurs in the mantle wedge, it is conceptually similar to the approach used by
experimental petrologists to simulate mantle melting (e.g., Grove et al, 2002), which
involve equilibration of a given bulk composition at various temperatures and pressures.
Figure 3.6 compares the fraction of melt produced at various temperatures for a
given starting H2O concentrations in the model mantle sources generated by addition of
fluid or melt. Melt fractions for both the hydrous-melt-fluxed and fluid-fluxed peridotite
cases are nearly indistinguishable. This suggests that the amount of H2O supplied to the
mantle strongly controls the degree of melting irrespective of whether the H2O is added
as a hydrous melt or a fluid. Slightly higher melt fractions are seen in the melt-fluxed
melting case, which may result from the additional fluxing effect of alkalis on the
peridotite solidus (Hirschman et al., 1998).
Figure 3.6. Percent melt and source H2O: results from pMELTS. Relationships between
the degree of partial mantle melting and amount of wt% H2O in the starting mantle
component at a range of temperatures calculate with pMELTS (Ghiorso et al., 2002). The
H2O in the mantle source (MM3; Baker and Stolper, 1994) was varied by addition of pure
H2O (black dashed lines) and hydrous eclogite partial melts (solid black lines; dacite
major element composition with 8 wt% H2O; Klimm et al., 2008).
45
Figure 3.7 shows the major element compositions of partial melts resulting from
various amounts of slab melt and aqueous fluid addition to the mantle wedge. For small
amounts of slab melt addition (1-5 wt%), the major element compositions of resulting
basaltic melts are similar to those of the aqueous fluid addition case. This shows that
equilibrium between partial melt and residual mantle largely controls the major element
composition of the final melt. Primary magma compositions calculated from the melt
inclusion data have compositions that overlap with the pMELTS model results (Fig. 3.7),
demonstrating that hydrous-melt-fluxed melting of the mantle wedge is a viable
explanation for the production of these magmas. However, when slab melt addition
exceeds 10%, the resulting high bulk H2O and alkali contents of the fluxed mantle wedge
source lead to higher melt fractions at a given temperature, and thus, exhaustion of
clinopyroxene occurs at ~1200C, producing melts with higher SiO2 at peak mantle
wedge temperatures. These high-Mg basaltic andesites may be analogous to natural high-
Mg basaltic andesite seen in the Lassen and Mt. Shasta regions (e.g., M. Clynne unpub.
data; Grove et al., 2002; Ruscitto et al., 2011).
Figure 3.8b displays the pMELTS model curves for Y and H2O for various
amounts of slab melt addition and temperatures. The H2Omax compositions and average Y
concentrations from the Lassen melt inclusions overlap with the model results and are
consistent with peak mantle wedge temperatures of 1300-1375C. The excellent
agreement between measured and modeled results, particularly with respect to H2O,
further supports the interpretation that the Lassen primitive magmas were formed by
variable addition of a hydrous slab melt component at similar peak mantle wedge
temperatures. Values of peak mantle temperatures overlap with those from Till et al.
46
(2012), which predicts temperatures of last mantle equilibration of ~1250-1350C.
Slightly higher temperatures determined in our study are likely the result of known
temperature over-predictions made by pMELTS of ~50 C when compared with
experimental methods (Ghiorso et al., 2002).
Figure 3.7. Comparison of pMELTS model results and melt inclusion compositions (in
eq. with Fo90 olivine; Table 2). a) H2Omax (calculated primary composition), b) K2O +
Na2O, c) CaO and d) Al2O3 wt% vs. SiO2 (all major elements normalized on a volatile-
free basis). Phase equilibria were calculated using pMELTS for a mantle source (MM3;
Baker and Stolper, 1994) mixed with either pure H2O (dashed lines) or a hydrous dacite
melt (solid lines; Klimm et al., 2008). Each line represent a model result from 900-
1400C at 1.5 GPa (normalized on a volatile-free basis).
47
3.5.5. The Sr/Y Adakite Signature
One hallmark characteristic of slab melt in arc magmas is high Sr/Y, caused by
melting in the presence of garnet, which makes up a large proportion of ecologitized
MORB in the downgoing oceanic lithosphere (Duffant and Drummond, 1990). During
ecologite melting, Sr is incompatible and increases in the melt phase, whereas Y is
compatible with garnet and retained in the downgoing slab. Most Lassen Region
magmas, however, do not display high Sr/Y values compared with the global array of
adakitic magmas (Fig. 3.8b). Using the same mixed mantle compositions and melt
fractions derived from the pMELTS models, melting curves in Figure 3.9b show that for
small amounts of slab melt addition (1-10%, similar to major element results), the Sr/Y
ratio is dampened due to the addition of Y from the spinel peridotite mantle component.
This yields values that overlap with values measured in melt inclusions from all but one
sample (BRM) from the Lassen segment (Fig. 3.8b). The results are consistent with
previous calculations from Kelemen (1993), which showed that peridotite-melt reactions
produced melts with lower LREE/HREE than the initial slab melts. The pMELTS models
results indicate that high Sr/Y adakitic signatures may only be retained in arc magmas if
slab melt addition is >10 wt%. Larger proportions of slab melt addition are thus required
to explain the high Sr/Y value of BRM, consistent with estimates of ~10% slab melt
addition derived from radiogenic isotope melting models (Fig. 3.5), and predictions that
this sample may have initially contained much higher H2O concentrations (Fig. 3.4). The
high-Mg andesites from the Lassen Region (M. Clynne, unpub. data) and the Mt. Shasta
region that have higher values of Sr/Y (~150; Ruscitto et al., 2011) could therefore be
produced by larger amounts of hydrous slab melt addition to the mantle wedge.
48
Figure 3.8. The effect of slab melt addition to peridotite for Sr/Y, Y and H2O. a) H2Omax
and b) Sr/Y with average Y for each cone (calculated primary compositions; Fo90; Table
3.1) with global range of adakites (GEOROC database), and experimental eclogite partial
melts (Klimm et at., 2008). Solid and dashed curves represent modeled mantle melt
compositions for various amounts of slab melt addition from 900-1300C at 1.5 GPa.
Modeled H2O composition derived as in Fig. 3.7. Modeled Sr and Y were calculated
using the batch melting equation for a mantle source (calculated for the Lassen sub-arc
mantle) mixed with 2, 5, and 10% (labeled on modeled curves) of a 5% partial melt of
Gorda MORB (Davis et al., 2008; partition coefficients from Kessel et al.,2005a; at 4
GPa, 1000C). Bulk partition coefficients calculated for a spinel peridotite assemblage
35/30/12/5-Ol/OPX/CPX/Sp (Hughes and Taylor, 1986) using mineral partition
coefficients of Eiler et al.(2005) for Sr and Eiler et al. ( 2001) for Y. Melt fractions
derived from pMELTS model results (for a given temperature and amount of slab melt
addition; Fig. 3.6).
49
Although most primitive Cascade arc magmas do not have particularly high Sr/Y
values compared to adakites, they do have other characteristics that indicate melting in
the presence of garnet when compared to the global array of basaltic arc magmas. For
example, primitive magmas from warm slab subduction zones, such as the Cascades,
Mexico, and western Aleutians, display elevated LREE/HREE (e.g., La/Yb; Walowski et
al, 2015) and coupled high 176
Hf/177
Hf and 143
Nd/144
Nd with lower values of Lu/Hf (Cai
et al., 2014) when compared with arcs associated with older oceanic crust. These
relationships demonstrate that partial melts of subducted oceanic crust play an
increasingly important role in the formation of magmas in arcs beneath which young
oceanic crust subducts.
3.5.6. Model for Melt Generation beneath the Southern Cascade Arc
Evidence provided by the geochemical results outlined above suggests that
southern Cascade arc magmas are produced by a multi-step process involving fluxing of
hydrous slab melts into the hot mantle wedge. Figure 3.9 shows a schematic
interpretation of this process that is based on the thermo-petrologic model results of
Walowski et al., (2015), the shear wave velocity model from Liu et al., (2012) and the
magnetotelluric resistivity data from Wannamaker et al. (2014). In our model, H2O is
retained in the hydrated upper mantle portion of the downgoing slab to greater depths
than that at which H2O is lost from the slab top (Fig. 3.9). Final chlorite breakdown
occurs in the slab interior when the slab top reaches ~75-80 km (Fig, 3.9; Walowski et
al., 2015). At this depth, the upper portions of the slab consisting of MORB-volcanics are
above the MORB+H2O solidus, and thus should melt when fluxed by rising chlorite-
50
derived fluids (i.e., Skora and Blundy, 2010; Till et al., 2012; Spandler and Pirard, 2013).
The resulting hydrous dacitic melts (Klimm et al., 2008; Jego and Dasgupta, 2013) then
rise into the overlying mantle wedge, and react with the surrounding mantle to produce
hydrous, calc-alkaline, basaltic to basaltic andesite melts.
As a further test of this model of magma formation beneath the southern
Cascades, we determined whether breakdown of chlorite can supply enough H2O to
balance the flux of H2O erupted from the Cascade arc. Previous work in the Nicaraguan
arc and northern Japan has provided evidence for hydration of the deep slab (Ranero et
al., 2003; Garth and Rietbrock, 2014) and the importance of fluids released from the deep
slab in the production of arc magmas (e.g., Spandler and Pirard, 2013). For the Juan de
Fuca plate, higher temperatures at Moho depths caused by the younger slab age may limit
the extent of serpentinization (Nedimovic et al., 2009), but no data are available for the
Gorda plate to assess upper mantle hydration. Because of this uncertainty, Walowski et
al. (2015) conservatively assumed 2 km of hydration below the Moho of the downgoing
plate and a bulk H2O concentration of 2 wt% for the hydrated peridotite. Using these
model parameters, the H2O flux contributed by chlorite breakdown in the slab interior is
estimated to be ~1-2 x 106 kg/km/yr. For the magmatic flux of H2O from the Cascades,
we use the estimate from Ruscitto et al. (2012). This method, which takes extrusive and
intrusive magmatic fluxes into account (Sherrod and Smith, 1990; White et al., 2006) and
utilizes primary volatile contents from the central Oregon Cascades (which overlap with
those from the Lassen region), yields a maximum H2O flux of 1.93 x 106 kg/km/yr. This
agrees very well with the flux resulting from our thermo-petrologic model, demonstrating
that fluids derived from the breakdown of chlorite in the hydrated upper mantle portion of
51
the slab may be sufficient to produce observed magmatic and volatile fluxes in the
Cascade arc.
The thermo-petrologic model results of Walowski et al., (2015) also predict two
main pulses of fluids from the downgoing slab associated with 1) the final breakdown of
hydrous phases during eclogitization of the oceanic crust, and 2) the final breakdown of
chlorite in the hydrated mantle portion of the slab (Fig. 3.9). The first, more shallow
pulse of fluid release correlates well with the location of low-resistivity anomaly beneath
the forearc (Wannamaker et al., 2014), and likely reflects a region of serpentinization of
the cold nose of the mantle wedge. The second predicted location, caused by the release
of the hydrous melt from the slab, agrees well with regions of low shear wave velocity
beneath the Lassen region (Liu et al., 2012). This is consistent with models of fluid
migration into the mantle wedge which suggest that, for most values of wedge
permeability, slab dip, and convergence velocity, there is a net migration of fluids and
melts away from the trench (Cagnioncle et al., 2007). This implies that arc magmas will
inherit a slab signature from a region of the slab that is slightly up-dip of the region that
lies directly beneath the arc. Therefore, patterns of decreasing amounts of a subduction
component towards the back-arc as observed in the geochemical data (Borg et al., 1997;
2002), provides further support for these interpretations.
52
Figure 3.9: Schematic interpretation for magma formation beneath the S. Cascades.
Chlorite-derived fluids from the deep slab interior beneath the forearc vents (small blue
arrows) drive flux-melting of the oceanic crust (red colored area), producing hydrous slab
melts that migrate into the overlying mantle (red arrows), where they react with peridotite
to induce further melting. The location of hydrous phase stability in the downgoing slab
(dark blue shaded region) and main pulses of fluid release from the slab (small light blue
arrows) are based on the thermo-petrologic model results of Walowski et al. (2015). Area
of low-velocity (dark and light orange shaded regions for latitudes 41 and 40.6,
respectively) based on shear wave velocity model of Lui et al. (2012). Green shaded
region shows the location of low resistivity from Wannamaker et al. (2014).
3.6. Conclusions
Our results provide strong evidence that magma production in the southern
Cascade arc is driven by hydrous slab melt addition to the mantle wedge. Low B
concentrations and MORB-like B isotope compositions indicate that extensive
dehydration of the plate occurs before it reaches sub-arc depths. However, the abundance
of volatile elements and correlation of volatile and trace element ratios (H2O/Ce, Cl/Nb,
Sr/Nd) show that Lassen region magmas have been enriched by variable amounts of
addition of a hydrous subduction component. Correlation of fluid mobile trace elements
53
and radiogenic isotopes demonstrates that the subduction component in the southern
Cascades is less radiogenic than the sub-arc mantle wedge, and must be derived from a
partial melt of the subducting Gorda MORB. pMELTS model results show that hydrous-
melt-fluxed melting of the mantle wedge can produce basaltic magmas with similar major
element compositions to those measured in Lassen melt inclusions. Agreement between
pMELTS model results and measured concentrations of H2O and Y confirms that
variations between magmas are likely formed by differences in the amounts of slab
component addition to the mantle wedge at peak temperatures of approximately ~1300-
1350C. Our results provide further evidence that chlorite-derived fluids from the deep
slab interior can flux-melt the oceanic crust, producing hydrous slab melts that migrate
into the overlying mantle, where they react with peridotite to induce further melting.
3.7. Bridge
In the preceding chapter (III), the compositions of olivine-hosted melt inclusions
from eight cinder cones were used provide evidence for slab melting and investigate
magma generation processes in the mantle wedge beneath the southern Cascades. In the
next chapter (III), I will focus on the youngest cinder cone in the Lassen region, Cinder
Cone (1666 C.E., Sheppard et al., 2009) to explore the melt evolution and plumbing
system dynamics prior to and during monogenetic eruptions in the southern Cascades.
54
CHAPTER IV
UNDERSTANDING MELT EVOLUTION AND THE MAGMATIC
PLUMBING SYSTEM AT CINDER CONE, LASSEN VOLCANIC
NATIONAL PARK, CALIFORNIA: INSIGHTS FROM OLIVINE-
HOSTED MELT INCLUSIONS
This chapter includes material co-authored with Dr. P.J. Wallace, Dr. K. V.
Cashman, J.K. Marks, Dr. M.A. Clynne, and Dr. Philipp Ruprecht. Sample collection was
performed by me with the help of Dr. Wallace, Dr. Cashman, J.K. Marks, and Dr.
Clynne. All melt inclusions were prepared and analyzed by me using Fourier transform
infrared spectroscopy (H2O and CO2), electron microprobe (major elements), and laser
ablation inductively coupled plasma mass Spectrometry (trace elements). Analyses, data
corrections, geochemical modeling, and interpretation were performed by me, with the
help of Dr. Wallace. This melt inclusion dataset is integrated with tephra stratigraphy,
componentry, and textural analyses performed by J.K. Marks (Marks, 2012). I drafted all
the figures used in this article and the text was written by me, with editorial assistance by
Dr. Wallace.
4.1. Introduction
Spanning approximately 1,250 km along the margin of the northwestern United
States and southern Canada, the Cascade magmatic arc is comprised of over 2,300
55
Quaternary volcanoes (Hildreth, 2007). Less than 30 of these volcanoes, however,
represent the most identifiable high peaks of the Cascades, while the majority of the vents
are small mafic shields and cones (Hildreth, 2007). In the Lassen area alone, over 500
monogenetic cinder cones and small shield volcanoes have erupted in the last 12 Ma
(Guffanti et al., 1990; Borg et al., 1997), and they collectively account for a large fraction
of the total erupted volume in the southern Cascades (Sherrod and Smith, 1990). Despite
the abundance of monogenetic volcanoes in the Cascades, and consequently, their
likelihood to pose volcanic hazards in the northwestern United States, these types of
volcanoes are understudied in comparison to the more evolved and longer-lived
stratovolcanoes.
Compositionally, monogenetic volcanoes in the Cascades are typically mafic, and
they can therefore be used as windows into mantle processes such as arc magma
formation (e.g., Borg et al., 1995, 1997; Leeman et al., 2004; Ruscitto et al., 2010;
Walowski et al., 2015). The eruptions of cinder cones typically last <1-15 years, and
these short timescales often result in limited evolution of their magmas. It has been
shown, however, that despite these short timescales, some cinder cones produce evolved
compositions and complex plumbing systems (e.g., Pioli et al., 2008). At Paricutin in
Mexico, for example, magmas evolved from basalt to andesite over the course of the
eruption that lasted ~9 years (McBirney et al., 1987; Luhr and Carmichael, 1985; Luhr,
2001; Rubin et al., 2004; Erlund et al., 2009). This compositional evolution was
accompanied by a decrease in explosivity and magmatic volatile contents, providing
insight into shallow storage reservoirs beneath cones in central Mexico (Pioli et al., 2008;
Johnson et al., 2008). At Cinder Cone, in Lassen Volcanic NP, CA, bulk compositions
56
also evolve systematically over the course of the eruption (Clynne et al., 2000). However,
this eruption occurred over a significantly shorter period of time, suggested to be less
than one year (Clynne et al., 2000; Sheppard et al., 2009). How do the compositions of
magmas from Cinder Cone evolve so rapidly? With a complicated inter-fingering of
tephra and lava flows, can we connect pre-eruptive changes in magma chemistry to
changes in eruption dynamics? What are the timescales associated with the formation,
storage, and ascent of these magmas?
To investigate these questions, we focus on the composition of olivine-hosted
melt inclusions sampled from the entire eruptive sequence at Cinder Cone. Melt
inclusions are small volumes of melt trapped inside of phenocrysts at depth, and as such
they can provide two unique insights in addition to traditional methods of bulk rock and
mineral chemistry. (1) Melt inclusions trapped in early crystallizing phases, such as
olivine, provide snapshots of melt chemistry, potentially before additional magmatic
evolution by fractional crystallization, mixing, and/or contamination occurs. In this way,
melt inclusions may provide better information about parental melt compositions, and
thus, better constraints on the processes of formation, storage, and evolution of the
erupted material. (2) Melt inclusions can be used to estimate pre-eruptive volatile
contents (e.g. and Wallace, 2008). The pre-eruptive concentrations of volatiles, such as
H2O, CO2, S, Cl, in a magma are key to understanding a variety of processes from mantle
melting (Gaetani and Grove, 1998; Grove et al., 2006; Hirschmann et al., 2009) to
magma ascent and eruption (e.g., Roggensack, 1997; Metrich and Wallace, 2008). Pre-
eruptive volatile contents are difficult to determine, however, because they decrease in
solubility as pressure decreases and therefore degas from the magma during ascent,
57
driving explosive eruptions, and leaving the erupted material with only a fraction of the
volatile contents with which it began (Holloway and Blank, 1994). Melt inclusions (MI)
are one of the best tools currently available to directly measure pre-eruptive volatile
concentrations, because they are trapped at depth, often before significant degassing
occurs. Because the solubility of H2O and CO2 in magmas is sensitive to pressure, their
concentrations within MI can also provide estimates of entrapment pressures (Newman
and Lowenstern, 2002; Papale et al., 2006; Iacono-Marziano et al., 2012), and therefore,
magma storage depths (e.g., Johnson et al, 2008; Pioli et al., 2008). Although recent work
has shown that melt inclusions are not perfect storage containers and can lose H+
(protons) by diffusion through the host and CO2 due to formation of a vapor bubble in the
inclusion, there are methods for distinguishing and correcting for these effects (e.g.,
Bucholz et al., 2013; Lloyd et al, 2013; Wallace et al., 2015).
In this study, we use major, trace, and volatile element concentrations in olivine-
hosted melt inclusions from the tephra deposit at Cinder Cone in conjunction with lava
and bulk tephra compositions and olivine major and trace element chemistry. We
interpret the data with regard to stratigraphic relationships between lava and tephra and
textural analyses of tephra clasts (Marks, 2012). We use these results to shed light on the
processes that led to compositional evolution of the magmas and accompanying changes
in eruptive dynamics at Cinder Cone. We show that the volatile contents of melt
inclusions can provide insight into the minimum depths at which these magmatic
processes occur. We also demonstrate the usefulness of melt inclusions in determining
the composition of the mantle source, in a case when the erupted bulk material is
sufficiently contaminated by crustal processes. Lastly, we estimate the timescales of
58
olivine residence times in the magmatic system to compare with the estimated timescale
of eruption. Using these results, we formulate a schematic model for the plumbing
systems beneath Cinder Cone.
4.2. Geologic Setting
Cinder Cone is a basaltic andesite scoria cone located in the northeast corner of
Lassen Volcanic National Park (Fig. 4.1). Lassen Volcanic National Park encompasses
430 km2 of volcanically-sculpted landscape surrounded by the Sacramento Valley and
Klamath Mountains to the west, the Sierra Nevada to the south, and the Basin and Range
to the east. The park gets its name from Lassen Peak, the tallest point in the national park,
a dacite dome complex that last erupted in 1915. Tectonically, Cinder Cone is found
within the Lassen Segment where volcanism is related to oblique subduction of the Gorda
micro-plate beneath the North American plate, producing the more abundant calc-
alkaline magmas (Clynne and Muffler, 2010). Tholeiitic magmas are also common in this
region, and are often associated with extensional faulting, the results of westward
expansion of the Basin and Range province impinging on the southern Cascade arc. The
quaternary volcanics in the Lassen region sit above older mafic to intermediate volcanoes
and volcanic products 2-4 km thick (Berge and Stauber, 1987). This volcanic basement is
underlain by plutonic Sierran and metamorphic Klamath terrain basement rocks as
suggested by mapped outcropping units (e.g. Saleeby et al., 1989; Cecil et al., 2012) and
constant modeled seismic velocities across the Sierra Nevada-Cascade Range boundary
(Berge and Stauber, 1987).
59
The eruptions and volcanic history of Cinder Cone have been an ongoing
controversy over the past century, and its eruption in 1666 A.D. was only recently
confirmed by radiocarbon dates of trees killed by the lava flows (Clynne, 2000).
Dendrochemistry and ring-width analyses of living trees were also utilized to determine
that the entire eruption likely occurred in less than one year (Sheppard et al. 2009). At
approximately 350 years old, it is the youngest cinder cone in the Cascade Arc and, as
such, has remained unvegetated allowing for excellent preservation of the lava flows and
tephra deposit (Clynne and Muffler, 2010). The eruptive material is comprised of a ~200-
meter-tall scoria cone built on top of an earlier cone, a tephra deposit as much as 3 meters
in thickness and ~20 by ~10 kilometers in spatial extent, and five main lava flows
separated into three phases – Old Bench, Painted Dunes, and Fantastic Lava (OB, PD,
and FL, respectively; Clynne and Muffler, 2010)(Fig. 4.1).
4.3. Sample Descriptions and Tephra Stratigraphy
The tephra deposit was first described in detail by Heiken (1978) and originally
separated into three phases, Units 1, 2, and 3, thought to correspond with the three phases
of lava flow emplacement, OB, PD, and FL, respectively. Samples used in this study
were collected from a ~1.2-m-deep pit to the north of Cinder Cone (Fig. 4.2; yellow star
in Fig. 4.1). Ten samples were collected from distinctive golden layers throughout the
section. Field descriptions of each sample are listed in Table 4.1, and a corresponding
field photo is labeled in Figure 4.2. The lowermost sample from the column, LCC-1-9, is
interpreted to be the opening phase of Unit 2, because it is thicker than the maximum
60
measured thickness of Unit 1 by Heiken (1978). Unit 2 is visually distinct from Unit 3 in
that it has appears to contain a higher percentage of larger golden tephra clasts. The Unit
Figure 4.1. Geologic and isopach map of Cinder Cone showing the distribution and
geology of the lava flows, and the whole-deposit tephra isopachs. The main tephra
column used in this study is shown as the yellow star. The three phases of the lava flows
are Purple = Old Bench (tephra Unit 1), orange = Painted Dunes (tephra Unit 2), and
green = Fantastic Lava (tephra Unit 3).
61
2 tephra deposit, calculated to have a minimum volume of ~0.6 km3, is also less
voluminous and widespread than Unit 3, which covers ~0.15 km3 (Marks, 2012). LCC-1-
5 is a dark fine ash layer which is interpreted to represent the boundary between Units 2
and 3, and also signifies a change in eruptive dynamics (Marks, 2012). The uppermost
layer, LCC-1-1, is overlain by a thin white layer of white 1915 Lassen Peak pumice.
There are several curiosities about Cinder Cone’s deposits and therefore its
eruption. First, there are ubiquitous quartz xenocrysts in all of the basalt-basaltic andesite
lava flows and tephra layers (Clynne et al., 2000). Second, the bulk composition of
erupted material changed from basalt to basaltic andesite through the PD flows and from
basaltic andesite to basalt through the FL flows (Clynne et al. 2011). The tephra mimic
these changes: tephra Unit 2 is compositionally similar to the PD flows and tephra Unit 3
is compositionally similar to the FL flows (Clynne et al. 2011).
Of the ten samples collected, six were chosen for melt inclusion analysis to best
represent the main eruptive phases. Tephra from LCC-9, LCC-7, and LCC-6 represent
the early erupted tephra, LCC-5, and LCC-4 are interpreted to represent the transition in
eruptive phases (closing phase of Unit 2 and opening phase of Unit 3, respectively), and
LCC-2 represents the late erupted tephra (Fig. 4.2). These samples were chosen to
understand the chemical transitions that accompany the textural changes of the tephra
deposit.
62
Figure 4.2. Stratigraphic section of sample locality. Field photo of the main tephra
column, with samples labeled and color-coded by tephra units. Colors will be used
throughout study. Descriptions can be found in Table 4.1 (Photo credit: K. Cashman.)
63
Table 4.1. Tephra Stratigraphy and Sample Descriptions Thickness Unit Description
-- -- A thin layer of 1915 pumice lies at the top of the section
10 cm LCC1-1 Coarse ash, vaguely laminated with abundant lava chips
2.5 cm -- Fine ash layer with abundant roots
2.5 cm -- Coarse ash layer
1 cm LCC1-2 Tan fine ash layer
15 cm LCC1-3 Two coarse ash layers separated by a thin fine ash layer
15 cm LCC1-4 Two coarse ash layers separated by a thin fine ash layer
2.5 cm -- Fine ash layer
17.5 cm -- Alternating cm-size layers of coarse and fine ash
2.5 cm LCC1-5 Fine ash layer that separates Fantastic Lava from Painted Dunes
1 cm LCC1-6 Tan Lapilli layer
5 cm -- Coarse ash layer of dark scoria intermingled with blond tephra
3.75 cm LCC1-7 Tan Lapilli layer
3.75 cm -- Dark ash with dense clasts
20 cm LCC1-8 Coarse tan lapilli layer, inversely graded. Base has abundant
oxidized cinder clasts
5 cm -- Dark coarse ash layer
12.5 cm LCC1-9 Coarse ash layer with mixed tan and black clasts
4.4. Methods
4.4.1. Sample Preparation
The ash sized fraction of tephra was used for the melt inclusion analyses because
it quenches more rapidly than lava flows, bombs, and lapilli sized tephra clasts,
minimizing the potential effects post-entrapment modification after eruption (Lloyd et al.,
2013). Loose olivine crystals, 1 mm to 250 μm in size, were hand-picked from the
washed and seived tephra. The olivine crystals were treated in HBF4 to remove adhering
glass and examined in immersion oils (refractive index 1.675) to locate melt inclusions.
Olivine crystals from the deposit are generally euhedral and all contain chrome-spinel
inclusions. Nearly all melt inclusions also contained a 10 to 30-μm-diameter vapor
bubble. Olivine hosting fully enclosed and glassy melt inclusions were mounted in crystal
bond on glass slides and prepared as doubly polished wafers. Wafers were immersed in
acetone to completely dissolve the crystal bond before Fourier transform infrared
64
spectroscopy (FTIR) analysis, and subsequently mounted in epoxy for electron probe
micro-analysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS) analyses.
4.4.2. Analytical Procedures
4.4.2.1. FTIR
H2O and CO2 concentrations were measured at the University of Oregon using a
Thermo-Nicolet Nexus 670 FTIR spectrometer interfaced with a Continuum IR
microscope. Concentrations were calculated from IR peak absorbances using the Beer–
Lambert law: C=MA/ρdε, where M is the molecular weight of H2O or CO2, A is the
measured absorbance of the band of interest (3550 cm-1
for H2O, and 1515 and 1435 cm-1
for CO2), ρ is the glass density at room temperature, d is the thickness of the MI wafer,
and ε is the molar absorption coefficient. An absorption coefficient of 63 L/mol cm
(Dixon et al., 1995) was used for H2O whereas the absorption coefficients for CO2 were
calculated for each inclusion based on the major element composition (Dixon and Pan,
1995). The background subtraction methods used to determine the carbonate peak heights
at 1515 and 1435 cm-1
are described in Roberge et al, (2005).
4.4.2.2. EPMA
Melt Inclusions and host olivine were analyzed for major elements, S, and Cl on
the Cameca SX-100 electron microprobe at the University of Oregon CAMCOR
MicroAnalytical Facility. MI glass compositions and host olivine were analyzed with a
10 nA, 10 μm diameter beam and 15 kV accelerating voltage for major elements. Time
65
dependent intensity corrections were made for Na, K, Si, and Al, and these elements were
analyzed first. Subsequently, the beam current was increased to 50 nA for collection of S,
Cl, Ti, and P. Individual inclusion analyses are averages of three point analyses. Olivine
compositions are also averages of three point analyses taken ~100 μm away from
inclusions and crystal edges to ensure analysis of olivine unaffected by later stage
diffusion.
4.4.2.3. LA-ICP-MS
Melt inclusions and host olivine were subsequently analyzed for a suite of trace
elements on the Photon Machines Analyte G2 193 nm ArF ‘‘fast’’Excimer Laser system
at Oregon State University, using 50 µm spot size with a 5 Hz pulse rate. Measured trace
element concentrations were determined by reference to GSE-1G glass as a calibration
standard and using 43Ca as an internal standard (see Loewen and Kent, 2012, for details).
BHVO-2G, BCR-2G, and GSD-1G glasses were also analyzed to monitor accuracy and
precision, and the analyzed values were within 10% of accepted values. A larger set of
olivine phenocrysts from LCC-2, LCC-4, and LCC-9 were analyzed at Lamont-Doherty
Earth Observatory. Data was acquired using a 193 ArF Eximer laser with a PQExcell
ICPMS operated in continuous line scan mode using a circular laser spot (25 µm for data
acquisition and 50 µm for pre-ablation) from the core to the rim of each olivine crystal.
Scan speed was 3 µm/s (30 µm/s during pre-ablation) and laser pulse rate was held at 15
Hz. Calibration curves were obtained using a set of reference glasses (BIR, BHVO,
GOR132-G and GOR128-G) for 15 elements (Li-7, Mg-26, Al-27, P-31, Ca-44, Sc-45,
Ti-47, V-51, Cr-52, Mn-55, Fe-57, Co-59, Ni-60, Cu-65, Zn-66). MPI-Ding Gorgona
66
glasses were specifically included to obtain good calibrations for element compatible in
olivine (most notably Ni). Mg-26 was used as internal standard. New calibration curves
were obtained prior to each sample. Reference glasses KL2-G and ML3B-G, and San
Carlos olivine (USNM 111312/444), were also analyzed to monitor accuracy and
precision.
4.5. Results
4.5.1. Olivine Compositions
The host olivines have core compositions of Fo88-90.5. A larger population of
analyzed olivine phenocrysts from LCC-9, LCC-4, and LCC-2 overlap with the MI host
olivine compositions (Fig. 4.3a), and exhibit broad, homogenous cores and thin Fe-rich
rims. From this larger population, 10 crystals were identified as xenocrysts because they
have variable zonation patterns and contain cores of Fo78-87 . These xenocrysts are
excluded from Figure 4.3 because they are not representative of the main phenocryst
populations. The olivine hosts for the analyzed melt inclusions have high core forsterite
compositions. Early erupted tephra have slightly more Mg-rich olivine cores (Fo89-90.5)
compared with the later erupted tephra (Fo88-89) (Fig. 4.3). Ealy- and late-erupted olivine
phenocrysts are also distinguished from each other in their trace element compositions
(Fig. 4.3b), with early-erupted olivine containing high Fo cores with a more restricted
range in Ni. These values are consistent with olivine previously analyzed from both lava
and tephra (M. Clynne, unpublished data).
67
4.5.2. Post-entrapment Crystallization and Fe-loss Corrections
The melt inclusions analyzed in this study were all sampled from rapidly
quenched tephra. However, melt inclusions are commonly affected by crystallization of
olivine along the walls of the inclusion and by Fe diffusive loss during the time between
trapping and eruption. If the measured composition of a melt inclusion is not in
equilibrium with the surrounding host olivine, then the melt inclusion has likely
experienced post-entrapment crystallization (PEC; Danyushevsky et al., 2000). The
original melt inclusion composition can be estimated by incrementally adding
equilibrium olivine back into the melt until it is in equilibrium with its host
Figure 4.3. Olivine phenocryst compositions. a) Fosterite content of olivine hosting
melting inclusions (filled symbols) and larger olivine population measured by LA-ICP-
MS (open symbols) ordered by relative stratigraphic height. See Table 4.1 and Fig. 4.2
for exact stratigraphic heights. b) Ni versus Fo for olivine phenocryst cores from the
larger population measured by LA-ICP-MS. This excludes olivine xenocrysts, as
described in main text. Solid black lines are fractionation curves labeled with tick marks
which represent 1% of olivine fractionation.
68
olivine (e.g., Ruscitto et al., 2010). In this study, Petrolog 3.1 (Danyuchevsky and
Plechov, 2011) was used to determine original melt inclusion compositions and to
calculate the percent of olivine crystallized from the melt inclusion after entrapment. For
this correction, Petrolog 3.1 used Fe-Mg partition coefficients (Kd) between the melt and
host olivine from Ford et al. (1983). Oxygen fugacity was determined using the
partitioning of V between the melt inclusion and host olivine using methods of Mallmann
and O’Neill (2009). The oxygen fugacities of the most primitive MIs were ΔQFM +1.4
(±0.4), with no distinct difference between eruptive units.
Post-entrapment crystallization corrections also require an estimate of the initial
Fe content of the MI prior to Fe-loss by diffusion. Bulk tephra analyses from Cinder
Cone were used as a proxy to estimate the original Fe contents. Primitive lavas in the
Lassen region have 7-8 wt% FeOT which overlaps with or is slightly higher than the
values for Cinder Cone lavas and bulk tephra (5.5-7 wt% FeOT). Based on this
comparison we assumed that Cinder Cone melts initially had 7 wt% FeOT. Volatile and
incompatible trace element concentrations in the melt inclusions were also corrected for
PEC using the Petrolog 3.1 results.
4.5.3. Major Element Compositions
We present data for 47 melt inclusions, 24 of which are from early units, 15 from
transitional units, and 8 from the late-erupted tephra. Corrected melt inclusions are
basaltic to basaltic andesite in composition (Fig. 4.4), and most fall in a narrow range of
SiO2 contents (51-53 wt% on a volatile-free basis). Variability in total alkalis, however,
shows compositional differences in MIs from different units. Early-erupted units (LCC-9,
69
LCC-7, LCC-6) have lower alkalis (~3.5-4 wt% Na2O+K2O) compared to middle- and
late-erupted units (LCC-5, LCC-4, LCC-2), which have higher values (~4-4.5 wt%).
Middle-erupted or transitional units (LCC-4 and LCC-5) display the most compositional
variability and contain the greatest number of inclusions that have higher concentrations
of both SiO2 and alkalis. This pattern is also apparent in the concentrations of other major
elements, such as MgO and CaO, which are elevated in early-erupted MIs compared to
late-erupted MIs, but highly variable in the transitional units (Fig. 4.5). Because early-
and late-erupted MI are easily distinguished with most major elements and are found
within tephra units that display distinct eruptive dynamics (Marks, 2012), for simplicity,
we will refer to the average early-erupted MI composition as magma batch 1 and the
average late-erupted MI composition as magma batch 2.
Most MIs have distinctly lower SiO2 than the lavas and bulk tephra (Fig. 4.4).
This is an indication, as will be discussed further below, that the magmas at Cinder Cone
were crustally contaminated after olivine growth and MI entrapment. Furthermore, most
olivine crystals (Fo89-90) are not in Fe-Mg equilibrium with the lava and bulk tephra and
often contain thin reaction rims of pyroxene (M. Clynne, unpublished data). We did not
analyze matrix glass, but the composition of olivine in equilibrium with the bulk tephra
(which is olivine enriched compared to the matrix) is Fo87-87.5. The olivine phenocrysts
rims are also commonly Fo88-87. Therefore, most olivine phenocrysts at Cinder Cone must
have grown from a more primitive parental magma before the magma became
contaminated. Interestingly, the differences in alkalis between early-erupted and late-
erupted MIs are mirrored in the total alkali concentrations of lava and bulk tephra (Fig.
4.4). Melt inclusions with elevated SiO2 (>54 wt%), which mostly come from the
70
transitional units, overlap with lava and tephra in MgO and Al2O3 content, and likely
represent melts that were affected by crustal contamination before being trapped in
olivine (Fig. 4.4 and 4.5).
4.5.4. Volatile Concentrations
H2O and CO2 concentrations measured in melt inclusions at Cinder Cone range
from 0.7-3.5 wt% and 0-1500 ppm, respectively (Fig. 4.6), similar to values for other
Figure 4.4. Melt inclusion total alkalis and SiO2 compared to bulk tephra and lava. Filled
symbols are melt inclusions from this study normalized on a volatile-free basis. Bulk lava
(open diamonds) and tephra (crosses) are unpublished data from M. Clynne.
Classification boundaries for basalt, basaltic andesite, andesite, trachy-andesite, and
trachy-basalt from LeBas et al., (1986). Uncertainty is less than the symbol size (See
Supplementary Table C.1; see Appendix C for all supplementary information for this
chapter).
71
Figure 4.5. Melt inclusion MgO vs. Al2O3 and CaO. MgO vs. a) Al2O3 and b) CaO for
MI compositions (normalized on a volatile-free basis) compared with lava and bulk
tephra (shaded blue region; M. Clynne unpublished data). Fractionation curves calculated
using Petrolog 3.1 for olivine (Ol, black dashed line; Danyushevsky and Plechov, 2011)
and Rhyolite-MELTS at 10 kbar for clinopyroxene (CPX, grey line; Gualda et al., 2012),
with tick marks representing 1% fractionation. Uncertainty is less than symbol size (see
Supplementary Table C.1).
72
nearby cinder cones Walowski et al., 2015; in prep.) and cones in the central Oregon
Cascades (Ruscitto et al. 2010; Ruscitto et al., 2011; LeVoyer et al., 2011). However, a
number of recent studies have shown that MI commonly experience post-entrapment
changes that decrease their dissolved H2O and CO2 concentrations (Esposito et al., 2011;
Gaetani et al., 2012; Bucholz et al., 2013; Lloyd et al., 2013; Hartley et al., 2014; Moore
et al., 2014; Wallace et al., 2014). The measured dissolved concentrations therefore
represent a minimum estimate of the initial H2O and CO2 contents of the magma during
entrapment.
Most basaltic MI, including nearly all MI in this study, contain a vapor bubble,
the size of which can be used to determine if it is primary (co-entrapped with melt) or
formed after entrapment (Riker et al., 2005; Aster et al., in prep.). Shrinkage bubbles
form after entrapment as a result of the pressure drop caused by crystallization along the
host-inclusion interface and thermal contraction of the melt (Roedder, 1979; Lowenstern,
1995). Because CO2 has a much lower solubility than H2O, it strongly partitions into the
bubble, leaving only a fraction of the CO2 dissolved in the melt compared to that at the
time of entrapment (Esposito et al., 2011; Hartley et al., 2014; Moore et al., 2014).
Recent work suggests that 40-90% of the total CO2 in the MI can be lost to this shrinkage
bubble (Moore et al., 2014; Wallace et al., 2014), leading to a drastic underestimation of
entrapment depths when only dissolved CO2 is taken into account. To correct for CO2
loss, we used a modified calculation based on the methodology of Riker (2005) and
Wallace et al. (2015). A comparison of this method with results of experimental
redissolution of CO2 in shrinkage bubbles and Raman spectroscopic determination of
CO2 densities in bubbles shows good agreement (Wallace et al., 2015; Aster et al., in
73
prep). First, we estimate the size of the vapor bubble at the time of eruption (Riker,
2005). This bubble volume is formed as the result of cooling-induced crystallization
(PEC) and melt contraction as a function of the change in temperature between
entrapment and pre-eruption (∆T). We use the phase equilibria of the most primitive melt
inclusion compositions calculated with rhyolite-MELTS (Gualda et al., 2012) and the
volume and thermal expansion data for silicate melts (Lange and Carmichael, 1990) and
olivine (Kumazawa and Anderson, 1968; Suzuki, 1975) to derive an equation for the
Cinder Cone magmas:
Bubble volume % = 0.0092 ∆T. Equation (1)
For each individual melt inclusion, we used Petrolog 3.1 to estimate the ∆T and then
equation (1) to estimate bubble volume %. Melt inclusions that did not contain a vapor
bubble were excluded from this correction. Although the absolute temperatures
calculated with Rhyolite-MELTS (Gualda et al., 2012) and Petrolog 3.1 (Danyushevsky
and Plechov, 2011) are different, the ∆T calculated for each MI from the two methods is
similar (Aster et al., in prep).
With this estimate of the pre-eruption bubble volume %, the pre-eruption
temperature, and the dissolved H2O and CO2 concentrations of each inclusion, we used
the VolatileCalc program (Newman and Lowenstern, 2002) to determine the pressure of
entrapment and the mol% CO2 in the equilibrium vapor phase. We then used the Redlich-
Kwong equation of state to determine the molar volume of CO2 in the vapor bubble. The
results of the CO2 restoration calculations suggest that 25-78% of the initial dissolved
CO2 in the MIs at the time of trapping was lost to vapor bubbles during post-entrapment
crystallization. Corrected concentrations of CO2 are shown in Figure 4.6.
74
The H2O contents of MIs can also be modified after entrapment. Experimental
studies have shown that at magmatic temperatures, olivine hosted MI can lose nearly all
of their H2O in hours to days via H+ (proton) diffusion, depending on temperature
(Gaetani et al., 2012; Bucholtz et al., 2013). To investigate whether some MI from Cinder
Cone had lost H by diffusion, we compared S/K2O and H2O/K2O ratios, because
correlated low values would indicate that lower H2O values in the MI were the result of
degassing of the melt before it was trapped (e.g., Johnson et al., 2010). However, the
inclusions show variable H2O/K2O with a more restricted range of S/K2O, and this
suggests the H2O variations may be the result of variable diffusive loss. For this reason,
we cannot employ the methods described in Lloyd et al. (2013) to infer original H2O
contents. Thus, to correct for post-entrapment H loss by diffusion, we assumed that all
melt inclusions initially had H2O/K2O values similar to that of the highest measured
value. This correction procedure should yield the maximum likely initial H2O content for
each inclusion. Melt inclusions that have >1 wt% K2O were not corrected for H-loss by
diffusion because they likely experienced crustal contamination, and may have been
trapped more shallowly after some degassing of H2O.
Trapping pressures for the restored H2O and CO2 concentrations were calculated
using solubility relations of Iacono-Marziano et al. (2012) and Papale et al. (2006). The
two methods gave similar trapping pressures, with values ranging from ~2-4.2 kbar for
the corrected MI (Fig. 4.6). These estimates are nearly 2 kbar higher than those estimated
from measured dissolved H2O and CO2 contents. Assuming an average crustal density of
2.6 g/cm2, these pressures represent entrapment depths of ~7-15 km below the surface.
Three melt inclusions did not contain vapor bubbles and were trapped more shallowly
75
(<2 kbar). Corrected melt inclusions fall more closely along open- or closed-system
degassing paths (Fig. 4.6), indicating that they may have been trapped at a range in
pressures, but this could simply be an artifact of our assumption of initially constant
H2O/K2O values (cf., Lloyd et al., 2012).
Figure 4.6. Melt inclusion corrected H2O vs. CO2. H2O wt% and CO2 ppm for corrected
(filled symbols) and measured/uncorrected (open symbols) MI, as described in the text
(Supplementary Tables C.1 and C.2). Inclusions without vapor bubbles do not require
this correction and were trapped at lower pressure. Isobars calculated using methods of
Papale et al., (2006) for an average melt inclusion composition. Open and Closed system
degassing paths calculated using the VolatileCalc program (Newman and Lowenstern,
2002). Error bars are one standard deviation.
4.5.5. Trace Element Concentrations
Melt inclusions at Cinder Cone have typical calc-alkaline, subduction-related
trace element patterns that are enriched in large ion lithophile (LILE) and light rare earth
(LREE) elements relative to high field strength elements (HFSE) like Nb and Ta (Fig.
4.7). MI from late erupted units have higher concentrations of highly incompatible
76
elements than early erupted MI (Fig. 4.7). MIs from transitional units that have elevated
SiO2 and alkalis are even more enriched in highly incompatible elements such as Sr, Ba,
U, and Pb (Fig. 4.7).
Figure 4.7. Spider diagram of average melt inclusions compositions. MI trace element
compositions corrected for PEC and normalized to depleted MORB mantle (DMM;
Workman and Hart, 2005). Blue and red shaded regions show the range in trace element
compositions for late- and early-erupted tephra, respectively. Black lines represent
individual melt inclusions from LCC-4 and LCC-5 that have higher SiO2 contents to
highlight trace element enrichments seen in these units.
4.6. Discussion
4.6.1. Crustal Contamination at Cinder Cone
The major element compositions of most MIs have distinctly lower SiO2 than the
lava and bulk tephra at Cinder Cone. This observation suggests significant chemical
evolution of the magma after olivine growth and melt inclusion entrapment. The
ubiquitous presence of quartz xenocrysts in the tephra and lava suggests that this
evolution was dominantly the result of crustal contamination. Partially melted and/or
77
vesiculated granitic clasts in the lavas (M. Clynne, unpublished data) likely represent the
source of the abundant quartz xenocrysts and rare K-feldspar xenocrysts.
Figure 4.8 shows the results of mixing calculations between the low-SiO2 melt
inclusion compositions and high-SiO2 compositions of the granitic xenoliths. Bulk tephra
and lava compositions fall along mixing lines between magma batch 1 (early-erupted MI)
and magma batch 2 (late-erupted MI) and the average granitic xenolith composition.
Early erupted PD lava and tephra can be produced by 10-35 wt% assimilation of granitic
basement by magma batch 1 (Fig. 4.8). Late erupted FL lava and tephra can be produced
by 15-30% assimilation of granitic basement by magma batch 2 (Fig. 4.8). Rare mafic
enclaves in the late-stage FL lava flows are similar in composition to the LCC-2 MI
compositions (M. Clynne, unpublished data), providing further evidence that the MI
represent the parental magma compositions. Unit 1 tephra, associated with the eruption of
the Old Bench lava flows, is compositionally similar to mildly contaminated early-
erupted Unit 2 tephra (which contains uncontaminated MI – samples LCC-9, LCC-7, and
LCC-6).
Melt inclusions from LCC-5 have TiO2 values that are more similar to the early-
erupted units or that fall along mixing lines with the early-erupted units. MI from LCC-4,
conversely, have TiO2 contents more similar to the late-erupted tephra. These
associations are consistent with our interpretations of the tephra stratigraphy, which
suggest that LCC-5 represents the final, waning phase of Unit 2, whereas LCC-4 is the
opening phase of Unit 3 (Fig. 4.2). LCC-5 also has the largest number of MIs that have
contaminated compositions, and which are similar to the lava flows and bulk tephra. This
may be related to the slowing of the eruption, which lead to shallow crystallization as the
78
Figure 4.8. Modeled mixing with granitic xenoliths. SiO2 vs. a) TiO2 and b) MgO
comparing MI compositions (normalized on a volatile-free basis; filled symbols) and
lava, bulk tephra, and quenched mafic enclaves (M. Clynne unpublished data). Curves
represent bulk mixing between granitic xenolith compositions (M. Clynne unpublished
data) and average composition of batch 1 (early-erupted MI; red dashed curve) and batch
2 (late-erupted tephra; blue dashed curve) parental magmas, see text for details. Tick
marks represent increments of 10% bulk addition of granitic material. Average analytical
uncertainty in upper right hand corner of each panel (see Supplementary Table C.1).
79
first eruptive phase came to a close. This slowing or waning of the first eruptive phase is
evidenced by increased groundmass crystallinity seen in the transitional tephra clasts
(Marks, 2012).
Further evidence for assimilation of granitic basement is provided by the trace
element compositions of MIs. Figure 4.7 shows that MI with elevated SiO2, which are
dominantly found in the transitional units, also have higher concentrations of
incompatible trace elements, such as Pb, Ba, U. These incompatible trace elements are
also found in high concentrations in the xenoliths and locally outcropping granitic
basement rocks (Wolf Creek Granite; M. Clynne, unpublished data), the likely source of
the xenoliths. The Li concentrations of the MIs appear to be particularly sensitive to the
granitic contaminant, correlating linearly with Pb (Fig. 4.9), and clearly separating MI
that have experienced contamination from those that did not.
4.6.2. Parental Melt Compositions
The olivine phenocrysts in the Cinder Cone tephra have compositions of Fo88-90.8
and the host crystals for the MI range up to Fo90.2. The upper end of the range of olivine
compositions overlaps with olivine that would be in equilibrium with mantle peridotite.
The trapping pressures of the MI, after accounting for CO2 lost to vapor bubbles and
possible H+ losses, are in the range of 2 to 4.2 kbar, providing evidence that the host
olivine crystallized in the middle crust. These observations require that either parental
melts in equilibrium with the mantle ascended into the middle crust without fractionating,
80
or that mantle sources beneath the Lassen region are relatively refractory, with olivines
>Fo90.
Figure 4.9. Melt inclusion Li vs. Pb corrected for PEC. High Li and Pb concentrations in
MI are indicative of addition of granitic material, and highlight melt inclusions which
sampled the contaminated magma. Errors can be found in Supplementary Table C.1.
Same symbols as in Fig. 4.8.
Late-erupted MI from LCC-2 show distinct compositional differences when
compared to early-erupted MI (Figs. 4.4 and 4.6), and are hosted in slightly less-
magnesian olivine (Fo88; Fig. 4.3), indicating that they could be related to the early-
erupted magmas via crystal fractionation. We used Petrolog 3.1 and pMELTS (Ghiorso et
al., 2002) to model equilibrium crystallization of the early-erupted magma at 4 kbar, the
maximum trapping pressure estimated from the corrected CO2 and H2O contents (Fig.
4.6). Olivine is predicted to be the liquidus phase for the primitive batch 1 composition,
but olivine crystallization alone cannot account for the decrease in CaO with decreasing
MgO that is observed (Fig. 4.5). Because these basaltic magmas are ultimately derived
from the mantle, they may have stalled near the base of the crust and undergone an
episode of higher pressure crystallization before ascent into the crust. Pressures near the
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Moho beneath the southern Cascades are ~10 kbar (~38 km; Mooney and Weaver, 1989)
a pressure above which clinopyroxene may replace olivine as the liquidus phase in
hydrous primitive basalts (e.g., Weaver et al., 2011; Blatter et al., 2013). Mass balance
modeling suggests that ~5% high-pressure clinopyroxene fractionation may explain the
observed major element differences between the two units (Fig. 4.5). However, phase
equilibrium calculations with pMELTS at 10 kbar for the composition of the early-
erupted magmas do not predict clinopyroxene as the liquidus phase, so we test this
possibility further using the trace element compositions of the uncontaminated melt
inclusions. Using equilibrium crystallization and partition coefficients between
clinopyroxene and basaltic melt for La, Nb, Sc and Th, we model how the melt
composition will change as the result of clinopyroxene fractionation. During
clinopyroxene fractionation, Sc is compatible and should decrease rapidly in the melt,
whereas Nb, Th, and La are incompatible, and should increase. For small amounts of
olivine and/or clinopyroxene fractionation, Nb, Th, and La will only increase slightly and
show little variability (Fig. 4.10 b, c, d). Figure 4.10 shows that 5% clinopyroxene can
explain the variability in Sc and the relatively constant Th concentrations between early-
and late-erupted units. However, the magnitude of Nb and La increases with decreasing
MgO wt% cannot be explained by fractionation alone. Thus, we suggest small amounts
of high-pressure clinopyroxene fractionation have likely affected the compositions of
batch 2 parental magmas, but conclude this processes cannot account for the differences
in trace element abundances between them. Because magma batches 1 and 2 are not
related solely by fractional crystallization, either in the mantle or in the crust, their subtle
82
differences are likely the result of mantle processes, such as variability in mantle source
composition or the degree of melting.
Figure 4.10. Melt inclusion MgO vs. trace elements. MgO (normalized on a volatile-free
basis) vs. a) Sc, b) Th c) La and d) Nb (PEC corrected) compared with lava and bulk
tephra (blue shaded region; M. Clynne unpublished data). Panels c) and d) exclude MI
with elevated Li and Pb, and determined to be contaminated. Fractionation curves
calculated using Petrolog 3.1. for MgO and the equilibrium crystallization equation and
appropriate partition coefficients for trace elements for olivine (Ol, solid grey line) and
clinopyroxene (CPX, dashed black line) with tick marks which represent 1%
fractionation. Partition coefficients were taken from Paster et al., (1974; Sc, CPX-basalt),
Beattie et al., 1994 (Sc, basalt-Ol, La, basalt-Ol), Hauri et al., (1994; Th., basalt-CPX, La,
basalt-CPX, and Nb, basalt-CPX), and McKenzie and O’nions, (1991; Th, basalt-OL, and
Nb, basalt-Ol). Average analytical uncertainty designated by symbol it top right corner of
each panel. Same symbols as in Fig. 4.8.
83
Compositional variability amongst olivine phenocrysts can further be used to
distinguish between early- and late-erupted parental magmas. Figure 4.3 shows the
olivine Ni and Fo core compositions and reveals differences in early- and late-erupted
units. LCC-9 has olivine phenocrysts cores with high Fo and a more restricted range in
Ni when compared with the late erupted units. Late-erupted olivine cores follow a steep
fractionation path (~2-3 % olivine fractionation) beginning with higher Ni, requiring
either a more refractory mantle source or presence of mantle pyroxenite (Straub et al.,
2011). The range in Ni of early-erupted olivine cores requires less than 1% fractionation
of olivine. Interestingly, some olivine phenocrysts from LCC-9, the earliest eruptive
phase, overlap with olivine from LCC-2 and LCC-4 (Fig. 4.3b). Given this similarity, it
seems likely that the lower-Fo olivine in LCC-9 were derived by interaction of batch 1
and 2 magmas (the latter represented by LCC-2 or LCC-4).
It is important to note that although magma batches 1 and 2 are distinct, they are
more similar to each other than to most other primitive basaltic magmas in the Lassen
region (Fig. 11; Clynne, 1995; Borg, 1995; Walowski et al., 2015). Walowski et al. (in
prep), show that most primitive magmas in the Lassen region are formed by variable
amounts of slab component addition to a relatively heterogeneous mantle wedge. Figure
4.11 shows that early- and late-erupted magmas have similar values of Sr/Nd, indicative
of similar amounts of subduction component addition (Walowski et al., in prep).
Differences in Nb/Zr, however, suggest that late-erupted magma batch 2 may be derived
from a slightly more enriched mantle source (Fig. 4.11). It is also possible that both
batches were derived from the same mantle source, but separated and experienced
different paths, down-temperature, through the upper-most lithospheric mantle. For
84
example, magma batch 2 may have reacted with pyroxenite veins in the uppermost
lithospheric mantle, which could explain the elevated Ni contents in olivine compared to
magma batch 1. Together, the observations demonstrate that monogenetic cones may tap
different batches of mantle-derived melts during a single, short-lived eruption (Brenna et
al., 2010, 2011; McGee et al., 2011). How these different magmas were tapped and where
they were stored, however, requires further analysis.
Figure 4.11. Comparison of Cinder Cone to Lassen region magmas. PEC corrected MI
compositions of Sr/Nd and Nb/Zr compared with other primitive lavas in the Lassen
Region (Borg et al., 1997). Symbol size for MI exceeds analytical uncertainty. Same
symbols as in Fig. 4.8.
4.6.3. Timescales of Mixing and Ascent
Olivine phenocrysts from all units typically have broad, homogeneous cores, and
Fe-enriched rims (Fig. 4.12). Because Ni is compatible in olivine and has a similar
diffusivity (Petry et al., 2004), it displays a similar pattern to Fe/Mg in the Cinder Cone
85
olivine phenocrysts. These Fe-rich and Ni-poor rims were likely developed during crustal
contamination, magma mixing or entrainment of olivine in new batches of melt,
processes that could lower the Mg and Ni content of the bulk magma. Although some
new olivine growth may have occurred, we can use the diffusion timescales of trace
elements, such as Ni, to estimate a maximum timescale of olivine residence in an evolved
magma prior to eruption.
The effect of diffusion on the Ni concentration in an olivine crystal can be
calculated with Fick’s second law, which describes the change in composition with time
over a one-dimensional system:
, Equation (2)
where C is concentration, t is time, and D is the diffusivity. The above expression of
Fick’s law assumes a constant diffusion coefficient, D, which for most natural systems is
an approximation. The diffusion coefficient for Ni in natural olivine, for example, varies
with temperature, pressure, oxygen fugacity and composition (Petry et al., 2004; Dohmen
& Chakraborty, 2007). We also assume that little to no olivine growth occurred during
the mixing event and as a result, our estimate will be a maximum timescale because
olivine growth is faster than Ni diffusion. The diffusion coefficient for Ni in the olivine
phenocrysts is assumed to be 2.6 x 10-16
m2/s, taken from Petry et al. (2004) for a
temperature of 1200C. For our boundary condition, we assume local equilibrium, that is,
the measured Ni content at the olivine rim is the equilibrium Ni content of the olivine
coexisting with the melt surrounding each olivine crystal. We also assume that the
average core composition is representative of the initial olivine core composition before
magmatic evolution (Fig. 4.12). To determine the best-fit diffusion curve, we calculated
86
diffusion profiles for a series of time-steps. The average of the two timesteps that were
visually determined to best bracket the measured Ni concentration gradient at the olivine
rim was used as the best timescale estimate (Fig. 4.12).
Figure 4.12. Ni diffusion in olivine. Panels a) and b) show examples of diffusion model
results as described in the text. Data points represent measured core-rim Ni contents
measured by LA-ICP-MS (symbols are the same as in Fig. 4.8). Model curves for 20
(black dashed curve) and 40 (solid black curve) days typically best fit the data. Panel c)
shows a probability density function of average model timescales for 7 different olivine
crystals from LCC-9, 6 from LCC-4, and 6 from LCC-2.
With these methods, we find that olivine phenocrysts from all units have an
average residence time of 20-40 days. Some phenocrysts have longer apparent
timescales, up to ~90 days, but uncertainty related to our model assumptions may cause
this discrepancy for a few olivine crystals. The largest source of uncertainty in this
method is derived from choice in temperature, and thus, diffusivity. Petrolog 3.1
87
estimates average trapping temperatures of ~1225C and pre-eruptive temperatures of
~1150C. This indicates that temperatures were decreasing during the mixing event,
which is not captured by our model. Decreasing the temperature would result in longer
timescales, however, our model also does not include olivine growth, which would
decrease the timescale.
The calculated residence times at Cinder Cone are much more rapid than those
calculated for olivine at Jorullo volcano in central Mexico (Johnson et al., 2008), which
suggested olivine residence times of 200 to more than 1000 days. This is consistent with
the total length of the eruption, as the eruption of Jorullo lasted for approximately 15
years (Luhr and Carmichael, 1985), whereas the Cinder Cone eruption probably lasted
less than 1 year (Clynne et al., 2000, Sheppard et al., 2009). Differences between mixing
and storage timescales and the eruption durations at Cinder Cone and Jorullo emphasizes
the diversity of complex behaviors that can be displayed at monogenetic cones. Although
there are large uncertainties associated with the calculated timescales, they still provide
some constraints for the processes associated with magmatic evolution prior to the
eruption of Cinder Cone. Importantly, our results demonstrate that the parental magmas
mixed with granitic crustal material very rapidly prior to eruption.
4.6.4. Mechanisms of Crustal Contamination and Plumbing System Evolution
Although the role of crustal contamination in formation of the erupted magmas at
Cinder Cone is clear, the mechanism by which this contamination occurred is more
difficult to decipher. Determining how contamination occurred can provide constraints on
how the magmatic plumbing system evolved prior to and during eruption.
88
Several, somewhat contradictory observations suggest two main hypotheses that
may explain the contamination of the Cinder Cone magmas: 1) A shallow, strongly
contaminated batch of magma, perhaps andesitic, was mobilized by and mixed with new
batches of magma coming from depth, or 2) an initial batch of magma thermally pre-
conditioned the granite, creating a zone of crystal- and xenolith-rich rhyolitic mush that
was quickly incorporated into the rising new primitive magma batches. In hypothesis (2),
there is no intermediate magma.
An important observation in support of hypothesis (1) is that granitic
contamination is ubiquitous, but the amount of contamination is heterogeneous and
changes throughout the course of the eruption. Specifically, Figure 4.13 shows the
temporal evolution of the SiO2 contents of the erupted tephra. For both eruptive phases,
magmas start off more evolved (andesitic), and become progressively less contaminated
over time. These temporal patterns in magma composition are similar to those observed
during eruptive episodes 2-47 of Pu’u ’O’o in Hawaii (Garcia et al., 1992; Wallace and
Anderson, 1998), and may indicate that a shallow, evolved magma batch was
simultaneously mixed with and pushed out of the conduit system by the ascending mafic
magma.
However, mineralogical or textural evidence for this contaminated magma seems
to be lacking. Olivine xenocrysts with lower-Fo cores may be representative of the
shallowly stored evolved magma. However, some of these xenocrystic olivine display
low-Fo cores and high-Fo shoulders (Costa and Dungan, 2005), as well as low-Ni cores,
high-Ni shoulders, and normally zoned rims, suggesting that they began to equilibrate
with the primitive parental magma before crustal contamination occurred (Fig. 4.14).
89
Two xenocrysts from unit LCC-4 do not have high-Fo rims, and have
significantly lower Fo contents than the other xenocrysts, and may be representative of
the mixed magma (Fig. 4.14). Conversely, these same crystals may have grown in the
contaminated magma during the waning and transitional period of the eruption, as they
are only observed in the transitional unit, LCC-4. In addition, we did not analyze olivine
less than 250 µm in diameter, and there could be a population of low-Fo olivine derived
from the contaminated magma in this size fraction. None of the analyzed MI have low-Fo
olivine hosts.
Figure 4.13. Temporal variability in bulk tephra compositions. All data in this figure is
unpublished data from M. Clynne, and depicts how tephra compositions change over the
course of the eruption at Cinder Cone. Unit transitions as defined by Heiken, (1978). The
Unit 1is equivalent to Old Bench. The opening phase of Unit 2 is equivalent to LCC-9.
The Unit 2-Unit 3 transition is equivalent to the transition between LCC-4 and LCC-5.
Melt Inclusions were not samples from Unit 1.
90
Figure 4.14. Core to rim variations in olivine xenocryts from LCC-9 (early-erupted; red),
LCC-4 (transitional; green), and LCC-2 (late-erupted; blue) tephra.
In support of hypothesis (2), lava and bulk tephra fall on mixing trajectories
between the granitic material and the two parental magma batches. If, for example,
magma batch 2 evolved as the result of mixing with the first batch of contaminated
erupted magma, one would expect mixing trajectories between magma batch 2 and the
contaminated magma of early-erupted units, which is not observed.
Using the combined observations presented above, we suggest the following
model for plumbing system evolution at Cinder Cone. First, one or several intrusions of
batch 2 magma enter the middle crust and form a set of small sills, which may be
partially integrated, over a range of depths. These batch 2 intrusions crystallize olivine,
and have variable compositions and trapping depths as evidenced by fractionation trends
in Fo vs. Ni (Fig. 4.3b). In a manner analogous to the model proposed by Grove et al.,
(1998) at Burnt Lava Flow, which involves the separation of heat and mass transfer, the
mid-crustal sills quench on their margins, and become mechanically separated from the
91
surrounding granitic basement. However, the sills may transfer heat to the surrounding
granitic wall rocks, causing them to variably melt or disaggregate. The shallowest sill or
sills then become contaminated, where some MI with contaminated compositions and
overlapping to lower trapping pressures are derived. Some of the unzoned xenocrysts
may also be sourced from various parts of this sill complex, such as the Fo77-79 (Fig.
4.14), that produced highly contaminated magma.
Batch 1 magma then rises from the deep crust or mantle. It interacts at least
partially with the existing sills because it samples olivine phenocrysts from batch 2
magmas, as suggested by Fo vs. Ni (Fig. 4.3b). A small portion of batch 1 magma
interacts briefly with the partially melted granite or contaminated magma, and erupts as
Old Bench lava flow and Unit 1 ash (these magmas are compositionally similar to early-
erupted lava and tephra; Fig. 4.8). Most of batch 1 magma stalls when it interacts with the
partially melted granite, mixing and crystallizing rims for 20-40 days. At this point, the
entire system becomes destabilized, and eventually erupts, with the most heavily
contaminated parts erupting first. As a result, the batch 2 sills also become destabilized,
causing them to ascend, interact with heated and partially molten granite, crystallize
lower Fo rims for !20-40 days, and finally erupt in a similar manner to the previously
erupted batch 1 magmas.
4.7. Conclusions
The eruption of Cinder Cone produced a series of tephra deposits and lava flows
that display complex changes in chemistry over the course of the eruption. High-Fo
olivine phenocrysts from all erupted units contain melt inclusions that are more primitive
92
in composition than the erupted material. The evolved compositions of the lava and bulk
tephra and the abundance of quartz xenocrysts within the deposits suggest the parental
magmas were rapidly contaminated by granitic material in the middle to upper crust. The
basaltic parental magmas sampled by the melt inclusions crystallized at minimum depths
of 2-4.2 kbar, which equates to approximately 7-15 km below the surface. Distinct
compositional variability between early- and late-erupted units suggest two different
mantle-derived basaltic magmas were tapped during the eruption. These two basaltic
compositions correlate with the two main explosive phases of the eruption, and were
separated by an eruptive slowing or pause evidenced by textural analyses of tephra clasts
(Marks, 2012). Diffusion modelling of Ni gradients in olivine rims suggests that olivine
residence times in an evolving magma were on the order of weeks, shorter than those
calculated for longer-lived cinder cone eruptions, such as Jorullo in Mexico. Temporal
changes in lava and bulk tephra compositions indicate that the granitic material was
heterogeneously incorporated after olivine growth and melt inclusion entrapment.
Although the geochemical evidence suggests that the parental magmas were
contaminated by either a shallowly stored evolved magma or a granitic mush, the exact
mechanisms that drove crustal contamination of the Cinder Cone magmas remain
enigmatic. Our combined results provide new insight into the complexities of short-lived
monogenetic eruptions.
93
APPENDIX A
CHAPTER II SUPPLEMENTARY MATERIALS
A.1. Methods
Cinder cones were chosen based on their primitive compositions to ensure
minimal contributions from crustal processes. At each cone, tephra deposits were
sampled to guarantee rapid cooling of olivine phenocrysts, thus minimizing the diffusive
loss effects that occur during slow cooling in lava flows. Olivine crystals ranging in size
from 1 mm to 250 µm were hand-picked from washed and sieved tephra. Fifty olivine-
hosted melt inclusions were analyzed for H2O and δD by NanoSIMS at the Carnegie
Institution of Washington. Olivine was polished on a single side to expose the inclusions
(50-250 µm in diameter) and pressed into an indium mount along with basaltic glass
standard grains, and gold coated for analysis (40 nm thick coat). Each inclusion was
analyzed once with a 10 nA Cs+ primary beam (~2µm diameter) rastered over a 20x20
μm area. Ion images were used during pre-raster to verify homogeneity of the analyzed
area and avoid beam overlap with surrounding olivine and vapor bubbles (if present).
NanoSIMS analysis of D/H ratios in glass generally followed the methods and
standardization described in detail in Hauri et al. (2006) but with NanoSIMS instrument-
specific modifications described here. We used a modified entrance slit of 60 µm width
to maximize transmission of H and D ions, paired with a standard aperture slit (350 µm
width). This combination resulted in a mass resolving power of ~1000; previous
measurements44
have shown that with good vacuum conditions and when using a Cs+
94
beam, H2/D ratios are typically <1.5x10-3
; this was verified at higher mass resolving
power prior to beginning analyses, with measured H2/D ≤1x10-4
. H and D were collected
on a Faraday Cup and electron multiplier, respectively; we also collected 18
O using a
Faraday cup. After presputtering and imaging to center the melt inclusion under the
beam without overlap onto olivine and/or vapor bubbles (where present), each isotope
was counted for one second per cycle, and we collected data over 300 total cycles for
each analysis. Faraday Cup backgrounds were measured off-peak 20 times every 80
ratios with the primary beam and electron beam on. Including presputtering, imaging and
measurement of signals and backgrounds, each analysis lasted approximately 15 minutes
and produced an average precision of ±3‰ (2M). Data were collected over 4 days of
analysis, and overall external reproducibility of the basalt glass standard GL07 D30-1
(1.5% H2O) was ±10‰ (2, n=32). D/H data were examined for matrix effects using a
two-collision cascade model described in detail in Hauri et al. (2006) but specific to the
NanoSIMS; the total range of matrix effects from hydrous rhyolite to low-H2O basalt on
the NanoSIMS are reduced (40‰) compared with the 6F ion microprobe (60‰), and
similarly it was found that for basaltic glass there are no resolvable matrix effects across
the range of H2O contents from 0.16 wt% to 2 wt% H2O (cf. Fig. 2.3 of Hauri et al.,
2006). Therefore we made no correction for matrix effects and simply corrected for the
instrumental mass fractionation (IMF) as determined by repeat analyses of GL07 D30-1
basaltic glass standard. The average precision of the IMF correction (±6‰ 2M of
standards run on each day, including uncertainty on known D/H ratio of GL07 D30-1)
was better than the overall external reproducibility; combining these uncertainties, we
estimate the typical uncertainty on a single SIMS measurement (precision + accuracy) is
95
±12‰ (2). Simultaneous measurements of H2O content were determined from the
measured 1H/
18O ratio calibrated against the standard glasses described in Hauri et al.
(2006), with uncertainties of ±6% (2).
The same inclusions were subsequently analyzed for a suite of trace elements on
the Photon Machines Analyte G2 193 nm ArF ‘‘fast’’Excimer Laser system at Oregon
State University, using 50 µm spot size with a 5 Hz pulse rate. Measured trace element
concentrations were determined by reference to GSE-1G glass as a calibration standard
and using 43
Ca as an internal standard45
. BHVO-2G, BCR-2G, and GSD-1G glasses were
also analyzed to monitor accuracy and precision, and the analyzed values were within
10% of accepted values.
A.2. Supplementary Discussion
Composition of the hydrous subduction component
The curves in Figure 2.2a show the compositions of melts that can be formed by
partial melting of the mantle wedge after variable amounts of a hydrous subduction
component have been added. A hydrous subduction component (fluid/melt released from
the slab into the mantle wedge) was mixed with a 10% partial melt of a depleted MORB
mantle (DMM; Workman and Hart, 2005) and a more enriched mantle (E-M; 66% DMM
and 33% enriched mantle; Donnelly et al., 2004), which reflect the range in relative
mantle enrichment of sub-arc mantle seen in the Lassen region (Supplementary Fig. A.2).
For the subduction component, we have used an H2O/Ce ratio calculated for the central
Oregon Cascades (Ruscitto et al., 2010) using the method of Portnyagin et al. (2007), and
the value is consistent with the relatively high slab-surface temperature predicted from
96
geodynamic models (Ruscitto et al., 2012). Because the concentrations of P2O5 in the
subduction component were not calculated by Ruscitto et al. (2010), we tried various
values, together with their maximum Sr concentration, until we achieved a good fit to the
data in Figure 2.2a. It is important to note that the absolute concentrations of elements in
subduction components calculated using the Portnyagin et al. (2007) method are poorly
constrained, as they result from summing the concentrations of all incompatible elements
(as oxides) plus H2O and Cl and then normalizing to 100%. The calculation does not
include SiO2 and many other major elements, so the concentrations of H2O and
incompatible trace elements would be quite different if the subduction component was a
hydrous silicate melt rather than an aqueous fluid. As a result, the mass fraction of the
subduction component added to the mantle along either of the curves in Figure 2.2a will
substantially vary depending on the fluid vs. melt-like character of the component.
However, the fraction of the total H2O in the final silicate melt generated in the wedge
that is contributed from the slab does not depend on this, and is a function only of the
initial mantle composition and the H2O/Ce content of the subduction component. For the
Cascades, the latter is well constrained from both geochemical data and geodynamic
models.
Calculation of slab surface temperatures
We use the H2O/Ce slab surface geothermometer (Cooper et al., 2012) for
comparison with temperatures calculated using a 2-D steady state thermal model (Wada
and Wang, 2009). The H2O/Ce ratio is a geochemical thermometer based on the
solubility of the REE-bearing phosphate minerals monazite and allanite (Cooper et al.,
97
2012). These phases occur within the top-most sediment layers of the slab, making
H2O/Ce a potential thermometer of the slab surface. Basalt melting experiments at sub-
arc slab pressures and temperatures suggest that allanite is also stable in basaltic oceanic
crust (Kessel et al., 2005; Klimm et al., 2008; Plank et al., 2009), and that its presence in
experimental run products is not an artifact caused by REE doping of the experiments
(Klimm et al., 2008). Our model for wet melting of upper oceanic crust basalt provides a
mechanism for re-equilibration of the more deeply sourced, trace element-poor fluids
derived from serpentinized mantle in the downgoing plate, with an allanite-bearing
basaltic crust. Although there is uncertainty as to the melt fractions at which allanite is
exhausted from the residue during wet melting of basalt, the slab surface temperatures
calculated using the H2O/Ce ratio are in agreement with the thermal model temperatures.
If re-equilibration of the mantle-serpentinite-derived fluids with a REE-bearing phase did
not occur, then apparent H2O/Ce temperatures would be much lower because serpentinite
derived fluids are H2O rich and trace element poor. It should be noted, however, that our
model and interpretations are based on the slab surface temperatures derived from the 2-
D steady state thermal model and do not rely on the correctness of the H2O/Ce
temperatures.
In the H2O/Ce temperature calculation, we assume that fluid and/or melt
migration from the slab and into the mantle wedge are vertical. However, recent work has
shown that fluids may migrate updip at the slab-mantle interface (if fluids are mobile)
and within the slab (if a permeability barrier exists at the interface) and also down-dip
with the subducting slab or the flowing overlying mantle (if fluids are relatively
immobile). The details of fluid migration paths predicted by currently available fluid
98
migration models (e.g., Wilson et al., 2014, Cagnioncle et al., 2007, Iwamori 1998, 2007)
vary widely, depending on the specific problems that are being investigated (e.g., some
combination of the effects of compaction, grain size, fluid availability, and melting) and
the assumptions and material properties used in the model. However, if lateral fluid
migration was taken into account, the effects would not change our general conclusions.
First, if up-dip flow was occurring (Wilson et al., 2014), then the fluids would be need to
be sourced from the slab down-dip of the arc. However, the thermal models predict that
no water remains in the slab past the arc. If metastability of hydrous minerals was
allowing water to be carried by the slab deeper than the arc, then the final stages of
chlorite breakdown would be occurring slightly down-dip of the arc, and the fluids rising
up-dip through the slab would have low D/H values. Second, in models that consider
lateral migration of fluids through the wedge once they are released from the slab
(Cagnioncle et al., 2007), the nature of the mantle wedge flow field controls the
migration. Initially, as fluids leave the slab-mantle wedge interface, they migrate in a
direction away from the arc trench because of down-dip flow of the wedge. But as the
fluids rise and trigger melting and the melts migrate through the upper part of the wedge,
the flow is directed back towards the trench because of the pattern of corner flow. Thus,
the two components of lateral migration partially offset each other. For most values of
wedge permeability, slab dip, and covergence velocity, there is a small net migration of
fluids and melts away from the trench (Cagnioncle et al., 2007), implying that arc
magmas will inherit a slab signature from a region of the slab that is slightly up-dip of the
region that lies directly beneath the arc. Overall then, the effects of some up-dip fluid
flow within the slab and lateral migration within the mantle wedge should partially offset
99
each other. For these reasons, we have chosen the zeroth-order assumption that fluid flow
is simply vertical, and this is a good starting point from which further studies and
modeling efforts can depart.
For both models, we also choose to exclude the latent heat of fusion during slab
melting. Assuming a 10% partial melt of the slab, the latent heat of fusion may cool the
system by ~50C. However, the type of discrepancy between H2O/Ce and geodynamic
model temperatures that we find for the southern Cascades (Fig. 2.2) does not occur for
the central Oregon Cascades (Ruscitto et al., 2010, and our new unpublished modeling),
where a very similar thermal structure should also lead to slab melting. The small offset
between the model temperatures predicted for the southern Cascades and the lack of
offset for central Oregon is precisely what Cozzens et al. (2012) predicted should occur
based on fluid flow modeling and heat flow measurements. We thus think it is a better
explanation for the small discrepancy between H2O/Ce and geodynamic model
temperatures in the southern Cascades. Given that the effect of including the latent heat
of fusion is relatively small and that other secondary factors that could cause similar
small increases or decreases in model temperatures have yet to be included in
geodynamic models, we have chosen not to try to incorporate this into our modeling.
Hydrogen diffusive loss corrections
Supplementary Figure A.3 shows the H diffusion loss corrections made for each
sample using the diffusive re-equilibration model from Bucholz et al., (2013). Melt
inclusion data for each cinder cone are shown in a panel with a histogram and a bivariate
plot. Each histogram shows the H2O concentrations (wt%) measured by FTIR for a larger
100
set of melt inclusions (Walowski and Wallace, unpublished data) than were analyzed by
NanoSIMS. Each panel also shows δD versus H2O (wt%) in melt inclusions measured by
NanoSIMS (Supplementary Fig. A.3). The curves show diffusion model results. For each
cone, the curves start at the maximum H2O concentration (defined as the average of the
highest 3-5 measured inclusions from the larger FTIR dataset), because these values are
assumed to be most representative of the starting, undegassed magma and are therefore
used as the starting value for the diffusive re-equilibration model. Model envelopes
represent variability in melt inclusion and host olivine size, both of which affect the
efficiency of diffusive loss. Starting δD for each model curve was varied in increments of
10‰ (colors shown in panel 1) to find model envelopes that best reproduced the
measured data points. The initial δD values shown in Figure 2.3a are the average of the
starting δD curves that fit the data, and uncertainties are reported as the upper and lower
limits of the starting δD values. Model corrections produce more negative values than are
measured at each cone. However, it is important to note that if the diffusion correction
was not performed and the lowest measured Lassen values were used to represent initial
δD, the values would still be distinctly more negative (isotopically lighter) than those
measured in the Marianas.
D/H Fractionation Model Calculations
The D/H fractionation model calculates the δD of the fluids released from the
downgoing slab using an equilibrium fractionation equation from White (2005),
11
(1 f ) ( f )
*1000
(Equation 1),
101
where ∆ is the difference in the δD of the residual material (or solid) from the initial δD
of the starting material, f is the fraction of H2O remaining in the solid after the reaction,
and α is the fractionation factor. Once calculated, ∆ is used to then calculate the δD of the
residual slab (solid) as,
δDsolid = δDinitial +∆ (Equation 2).
Because the system is assumed to be in equilibrium, we can then use the definition of
alpha,
α = (δDsolid +1000) / (δDfluid +1000) (Equation 3),
to calculate the δD of the fluid as,
δDfluid = ((δDsolid +1000) / α) – 1000 (Equation 4).
The fraction of H2O remaining in the slab, f, was calculated by adopting the
approach developed by Wada et al., (2012). We use a generic lithologic model and initial
bulk H2O concentrations as described in Hacker (2008) and assume localized hydration in
the incoming oceanic plate (as opposed to uniform hydration; Wada et al., 2012). For the
Lassen Region, we use an incoming plate age of 8 Ma, a maximum depth of decoupling
of 75 km, and 2 km thick hydrated upper mantle, while in the Marianas case we assume a
4 km thick hydrated upper mantle (for other thermal model parameters, see Wada and
Wang, 2009, for the Cascades and Marianas). The modeling results for .the distribution
of H2O remaining in the slab are shown for the Lassen Region (Fig. 2.3b) and the
Marianas (Supplementary Fig. A.4). These results are consistent with calculations from
Van Keken et al., (2008). The starting δD values, δDinitial, were based on measured values
of natural samples for MORB and gabbro (-50‰; Agrinier et al., 1995) and serpentine in
102
mantle peridotite (-60‰ to -40‰; Barnes et al., 2009; Alt and Shanks, 2006). The
fractionation factor, α, is calculated using a series of experimentally derived factors of
important hydrous phases found in the slab lithologies (Supplementary Fig. A.5).
Uncertainty in starting δD values (±10‰) and fractionation factors (Supplementary Fig.
A.5) result in an approximate error of ±15‰ (2σ) after propagation.
Previous work, dominantly in the Nicaraguan Arc, has provided evidence for the
hydration of the deep slab (oceanic peridotite up to ~20km depth; Ranero et al., 2005),
and the role of these fluids during the production of arc magmas (Barnes et al., 2009).
Furthermore, our model yields predictions that are very similar to values calculated for
fluids in equilibrium with exhumed chlorite-bearing harzburgites from Cerro del Almirez,
Spain, that have been interpreted to represent subducted oceanic peridotite. Alt et al.
(2012) calculated that fluids in equilibrium with these chlorite-bearing harzburgites at
700C had δD values that ranged from -65 to -27‰. This calculation employed the same
fractionation factors used in our study (Graham et al., 1984b, Graham at el. 1987), and
our methodologies only differ in that we model progressive dehydration. In our model for
the Cascades, 700C is reached in the hydrated upper mantle portion of the slab when the
slab surface is at ~60-65 km depth, at which point we predict δD of fluids released from
chlorite-bearing harzburgite to be -55 to -30‰, overlapping values from Alt et al. (2012).
However, because fractionation becomes more extreme as H2O concentrations decrease
in the peridotite at higher temperatures, large variations in δD in the released fluids occur
over a relatively small range in temperature. Our temperatures in the subducted mantle
beneath the arc are ~770C, producing fluids with δD values that range from
approximately -100 to -80‰, which overlap with Cascade melt inclusion values.
103
Large-scale hydrogen isotope fractionation during fluid and/or melt transport
Hydrogen isotope fractionation could potentially occur by diffusion as fluids
and/or melts migrate through the slab and wedge. Indeed, this is the large-scale
equivalent of the process we observe and correct for in the melt inclusions (post-
entrapment H loss). But the significance of this process on the large scale is entirely
dependent on whether the H2O flux is dominantly diffusive or dominantly advective. We
postulate that veining within exhumed terrains that represent subducted oceanic
lithosphere (John et al., 2008; 2012) is evidence for dominantly advective fluid flow
within the slab and superjacent mantle wedge, and so, in our model we ignore diffusion
during large-scale dehydration of the slab. Fluid and melt transport within the mantle
wedge are also likely to be dominated by advective flow (Wilson et al., 2014, Cagnioncle
et al., 2007, Wada et al., 2012).
Sr isotope evidence for slab melting
In many arcs, basaltic magmas have variably elevated 87
Sr /86
Sr ratios that have
been interpreted to result from subduction recycling of seawater-derived Sr (e.g. DePaolo
and Wasserburg, 1977). However, in the southern Cascades, we observe negative
correlations between 87
Sr /86
Sr and subduction component indicators, opposite of what is
commonly observed in arcs (Supplementary Fig. A.6). The trend for the southern
Cascades requires a subduction component with unradiogenic 87
Sr /86
Sr (Borg et al.,
1997), which we suggest may be derived from partial melting of the downgoing basaltic
crust. This interpretation relies on the observation that oceanic crust is heterogeneously
104
altered during hydrothermal alteration (e.g., Bach et al., 2003). Hydrous phases that form
during this alteration should acquire elevated 87
Sr /86
Sr values, whereas unaltered portions
should retain a MORB-like signature. Because hydrous phases are exhausted at the
eclogite transition, before the plate reaches subarc depths beneath the Cascades, much of
the radiogenic Sr that was added to the oceanic crust by hydration will likely be lost to
the forearc mantle wedge. Fluids from serpentine and chlorite dehydration within the slab
interior should have a seawater Sr-isotope signature, but are solute poor, and as a result
have little leverage when mixed with more Sr-rich, unradiogenic, partial melts of
eclogites (Spandler et al., 2014; Klimm et al., 2008).
105
Supplementary Table A.1. Bulk Tephra Analyses
Sample BBL-05MI BORG-1 BPB-1 BAS-44-02 BPPC-01 BRVB-01 Cinder ConeMI
Lat (N) 40°34'33.72" 40°39'15.63" 40°40'40.80" 40°37'50.64" 40°19'34.22" 40°31'48.78" 40°32'24.50"
Long (W) 121°37'1.32" 121°13'29.07" 121°12'51.00" 121°20'40.14" 121°54'38.64" 121° 4'34.32" 121°18'37.00"
wt%
SiO2 49.76 49.29 52.44 50.04 51.83 50.38 51.85
TiO2 1.04 0.64 0.92 1.00 0.82 1.32 0.83
Al2O3 17.27 15.48 17.16 17.80 16.78 16.86 16.61
FeOt 9.38 8.54 7.65 8.88 7.68 9.39 6.88
MnO 0.14 0.15 0.14 0.16 0.15 0.16 0.09
MgO 8.38 8.05 8.76 9.01 9.14 8.65 9.68
CaO 10.34 8.50 9.35 9.92 10.60 9.24 10.02
Na2O 3.14 2.07 2.69 2.67 2.56 2.90 3.05
K2O 0.37 0.40 0.71 0.36 0.34 0.84 0.84
P2O5 0.18 0.10 0.19 0.16 0.10 0.27 0.15
CO2max
(ppm) 856 1199 614 721 1010 570 1138
H2Omax 1.33 3.30 3.23 1.17 2.44 2.67 3.46
Olivine Fo
content* 85.13 88.20 86.48 87.71 87.32 84.45 89.84
ppm
La 7.62 5.54 11.70 8.75 6.30 14.06 7.46
Ce 18.6 13.2 25.7 21.2 15.1 32.0 16.9
Pr 2.60 1.82 3.49 3.03 2.18 4.44 2.31
Nd 11.9 8.16 14.8 13.3 9.77 19.2 10.5
Sm 3.35 2.20 3.51 3.40 2.67 4.58 2.41
Eu 1.18 0.76 1.14 1.17 0.95 1.48 0.80
Gd 3.93 2.29 3.48 3.63 3.04 4.58 2.47
Dy 4.60 2.48 3.41 4.12 3.45 4.46 2.55
Er 2.81 1.39 1.88 2.46 2.12 2.42 1.39
Yb 2.66 1.31 1.68 2.27 1.95 2.12 1.39
Ba 146 154 309 151 125 337 202
Th 1.47 1.07 1.90 1.08 0.69 1.83 1.63
Nb 3.87 2.48 5.61 3.11 1.81 7.06 4.03
Y 24.6 12.9 17.5 22.0 18.9 22.9 13.1
Hf 2.63 1.61 2.53 2.33 1.83 2.91 1.73
Ta 0.25 0.17 0.37 0.20 0.12 0.45 0.26
U 0.44 0.33 0.57 0.34 0.23 0.55 0.52
Pb 3.32 2.48 3.84 2.66 1.89 3.44 3.22
Rb 8.68 7.40 14.60 7.24 6.25 16.03 15.39
Sr 186 362 464 411 461 459 342
Sc 41.4 28.8 30.2 36.7 36.0 30.1 27.1
Zr 104 60.1 98.5 89.3 67.2 114 70.9
MI – Values represent average of the most primitive measured melt inclusion compositions because bulk tephra
analyses were not available
*Average Fo content of all host-olivine of analyzed melt inclusions
Sample names are abbreviations based on Clynne and Muffler (2010): BBL = Basalt of Big Lake; BORG = Basalt of
Old Railroad Grade 3; BPB = Basalt of Poison Butte 3; BAS-44 = Basalt of Highway 44; and unpublished locations:
BPPC = Basalt of Paynes Creek Parasitic Cone; BRVB = Basalt of Round Valley Butte.
Locations are based on NAD27 datum used in Clynne and Muffler (2010). Additional geochemical data for most
samples can be found in Clynne et al. (2008); Borg et al. (1997, 2002, 2000); Clynne (1993).
106
Supplementary Figure A.1. Bulk tephra trace element compositions. Trace element
compositions from bulk tephra of analyzed cones in the Lassen Region compared to
previously published endmembers. Low and high Sr/P represent endmember CABs with
variable amounts of a subduction component (Borg et al., 1997). The high-alumina
olivine tholeiite (HAOT, sometimes called low-K tholeiites; Bacon et al., 1997) is an
endmember composition of tholeiitic magmas from the Lassen region, associated with
normal faulting in the back-arc, which are not influenced by subduction enrichment.
Although some magmas used in this study have low K2O, they are more enriched with
respect to incompatible trace elements than the HAOT magmas, indicating that they are
enriched by a subduction component.
107
Supplementary Figure A.2. Relative source depletion and subduction enrichment
Nb/Zr versus H2Omax/Ce showing the relative depletion of the source mantle (N-MORB
and E-MORB; Sun and McDonough, 1989; Michael, 1995) of the samples and effects of
subduction enrichment. The relative depletion of the mantle source seen in this figure is
used as the basis for calculating a range in starting mantle components used in Fig. 2.2a
and discussed in the Supplementary Materials. This figure also highlights that increased
addition of a slab component results in higher H2O/Ce (and therefore (Sr/P)N) and in
conjunction, creates source variability and across-arc trends seen in the Lassen region
primitive basalts.
108
Supplementary Figure A.3. Corrections for effects of diffusive loss from melt
inclusions for each cone using the model of Bucholz et al., (2013). A panel for each
cinder cone contains a histogram (H2O concentrations measured by FTIR from a larger
set of inclusions) and a bivariate plot of δD versus H2O. Open circles are individual melt
inclusions measured by NanoSIMS, and colored curves are diffusion model results (color
based on starting δD shown in panel 1). The starting point for each model, H2Omax,
represents the average of 3-5 melt inclusions with the highest H2O measured by FTIR.
109
Supplementary Figure A.4. a) Model results showing the distribution of H2O remaining
in the downgoing slab for the Marianas Arc and b) the cumulative H2O released from the
slab for both the Marianas and the Cascade Arc. Hydration of incoming plate is based on
those previously used in Wada et al., (2012).
110
Supplementary Figure A.5. Experimentally derived fractionation factors (1000ln)
versus temperature for minerals found in a) MORB and gabbro and b) serpentinized
mantle. Fractionation factors used are for hornblende (Suzuoki and Epstein, 1976;
Graham et al., 1984a), epidote (Graham et al., 1980; Chacko et al., 1999), chlorite
(Graham et. al., 1984b), and serpentinite (Sakai and Tatsumi, 1978). In Fig. 5a, large
overlaps are seen between experimental results of similar phases, and thus individual
experimental data points are plotted along with best fit curves for each set of
experiments. The dashed line represents a best fit polynomial regression for all of the
data. Because of the range in fractionation factors for similar phases, we use the
regression that represents an average rather than calculating modal abundances of
minerals present in each lithology. The 2σ curves were used to calculate the total
uncertainty in the model contributed by the fractionation factors. For Fig. 5b, serpentinite
and chlorite are the only two phases for which fractionation factors exists, and the
temperature range over which experiments were performed do not overlap. Therefore, the
model uses serpentinite for T<500C and chlorite for T>500C.
111
Supplementary Figure A.6. Sr isotopes versus mantle normalized Sr/P for basalts in
different Cascade Regions. Variation in 87
Sr/86
Sr in the Mt. Adams region (Jicha et al.,
2009) does not show negative correlations seen in the southern Cascades, likely due to a
distinct difference in mantle source composition, evidenced by abundant OIB-type
magmas in the southern Washington Cascades.
112
Supplementary Figure A.7. Garnet signature in hot-slab subduction zones H2O/Ce
versus La/Yb from the global database of Ruscitto et al., (2012). Lassen Region data
points are averages of each cinder cone analyzed in this study.
113
A.3. Hydrogen Isotope and Trace Element Compositions
The following table contains analyzed values for individual melt inclusions. H2O
wt% and δD were measured by NanoSIMS, and trace elements weremeasured by LA-
ICP-MS, as described in section A.1.
The range in PEC* listed in the table gives the calculated range in post-
entrapment crystallization (PEC) from a larger dataset of melt inclusions from the same
cinder cones (Chapter III). Major element compositions for the melt inclusions and host
olivine were not determined out for these inclusions, and we are therefore unable to
correct for post-entrapment modification. However, in the manuscript, we focus on
volatile and trace element ratios which should not be affected by PEC.
114
BORG S-17 S-13 S-12 S-15 S-09 S-10 S-05 S-06 S-07 S-08 S-01 S-04 S-03
δD (‰) -11.0 -31.4 -47.9 -29.1 -58.8 -38.7 -42.0 -53.5 -25.1 -26.4 -63.4 -66.8 -48.8
H2O
(wt%) 2.37 2.93 2.51 2.61 2.71 2.54 2.62 2.85 2.44 2.67 3.01 2.92 2.94
Range in
% PEC*
0.20 - 7.5
(ppm)
Li 9.49 6.11 5.19 5.78 4.77 4.61 10.91 10.03 9.65 7.43 5.91 5.64 8.02
B 4.52 3.52 2.95 3.12 4.41 3.13 5.21 5.54 7.28 2.85 1.70 4.78 3.64
P 819 660 710 739 584 605 1291 1096 1009 726 320 1257 685
Ti 5633 4679 4695 4463 4016 4176 4081 6019 6334 4771 1550 7092 4562
V 236 236 318 237 242 262 348 289 288 249 164 307 257
Cu 305 78 110 174 104 103 152 129 369 110 96 138 112
Rb 8.20 5.36 6.03 5.10 4.72 4.95 7.95 7.84 9.78 5.88 1.53 10.25 5.10
Sr 660 533 487 353 410 411 368 602 707 523 541 635 422
Y 15.08 13.03 12.95 13.13 11.68 11.72 12.93 16.00 14.95 13.66 4.60 16.79 12.14
Zr 59.68 53.91 49.88 59.87 46.65 44.87 57.34 65.80 67.88 53.66 14.94 81.60 50.48
Nb 1.78 2.20 2.24 2.33 1.85 1.82 1.59 3.40 2.07 2.15 0.58 3.74 1.93
Ba 230 179 178 125 130 125 138 228 285 177 54 262 135
La 6.65 5.65 4.64 4.46 4.25 4.51 5.09 6.69 7.88 5.39 1.70 8.20 5.07
Ce 15.48 13.05 13.14 11.79 10.73 11.01 13.93 17.01 18.02 13.73 3.94 20.16 13.35
Pr 1.99 1.87 1.77 1.50 1.57 1.56 1.64 2.54 2.41 1.73 0.52 2.96 1.64
Nd 10.23 9.10 9.36 8.80 7.14 7.61 7.84 11.25 12.65 8.54 2.49 12.19 9.29
Sm 2.65 2.51 2.04 1.84 1.75 1.68 1.33 2.67 1.99 2.53 0.44 2.09 2.27
Eu 1.05 0.82 0.79 0.82 0.61 0.73 0.33 0.86 1.12 0.73 0.27 1.17 0.85
Gd 2.53 2.16 1.94 2.34 2.03 2.37 3.77 3.10 3.10 2.76 0.53 2.90 2.71
Dy 2.16 2.15 2.23 2.41 2.26 2.09 2.18 2.91 2.93 2.71 0.51 2.89 2.10
Er 1.43 1.33 1.47 1.38 1.35 1.41 N/A 1.65 1.69 1.73 0.50 1.91 1.32
Yb 1.75 1.63 1.65 1.36 1.22 1.24 N/A 1.67 1.42 1.03 0.47 1.60 1.45
Hf 1.95 1.28 1.35 1.26 1.23 1.09 1.10 1.21 1.78 1.31 0.32 1.58 1.50
Ta 0.07 0.12 0.12 0.11 0.05 0.09 N/A 0.13 N/A 0.05 N/A 0.14 0.07
Pb 4.28 2.90 3.42 1.71 2.38 2.50 2.27 3.46 5.17 2.86 0.82 5.09 3.23
Th 0.93 0.87 0.48 0.68 0.56 0.59 0.80 0.92 1.30 0.69 0.26 1.05 0.60
U 0.37 0.15 0.29 0.21 0.22 0.14 0.38 0.30 0.49 0.08 0.05 0.49 0.26
115
BBL BBL-S-
06
BBL-S-
11
BBL-S-
08
BBL-S-
05
BBL-S-
04
BBL-S-
02
δD (‰) 5.17 -63.49 -59.52 -60.22 -79.41 -39.71
H2O
(wt%) 0.905 1.291 1.304 1.194 1.318 1.268
Range in
% PEC* 2.2-6.6
(ppm)
Li 6.59 5.75 5.04 6.05 10.25 12.15
B 1.38 0.63 1.38 6.23 2.64 N/A
P 874 942 973 3384 857 1237
Ti 5299 6266 6196 13031 5464 7100
V 206 202 219 310 217 259
Cu 151 58 83 75 71 114
Rb 3.67 4.85 5.23 16.51 3.54 7.20
Sr 226 262 256 387 251 266
Y 19.22 21.84 20.74 32.97 19.29 25.20
Zr 60.52 79.48 74.09 194.35 71.64 97.29
Nb 1.77 2.60 2.48 9.24 1.93 3.35
Ba 105 146 146 428 134 189
La 4.05 6.04 5.81 17.44 5.63 7.35
Ce 11.16 14.42 16.08 39.22 15.18 20.04
Pr 1.60 2.05 2.14 5.25 1.94 2.71
Nd 7.90 10.46 8.66 24.34 9.68 11.94
Sm 2.23 3.39 2.89 5.39 2.62 3.25
Eu 0.82 1.04 1.00 1.63 1.02 1.09
Gd 2.13 3.54 2.97 5.72 3.15 3.79
Dy 3.44 3.53 3.33 6.09 3.21 4.08
Er 2.00 2.42 3.00 3.80 2.37 2.41
Yb 2.14 2.50 3.27 3.50 1.77 3.26
Hf 1.51 1.68 1.97 4.90 1.45 2.30
Ta 0.10 0.16 0.09 0.61 0.13 0.20
Pb 1.85 1.85 1.92 6.02 1.86 3.58
Th 0.33 0.44 0.46 1.72 0.20 0.76
U 0.07 0.14 0.16 0.64 0.21 0.21
116
CC S-09-
1
S-09-
5
S-09-
6
S-09-
7
S-09-
9
S-02-
6
S-02-
10
S-02-
3
S-02-
1
S-02-
8
δD (‰)
-
57.67
-
37.78
-
46.69
-
61.28
-
22.13
-
82.82 -50.95
-
71.94
-
60.02
-
55.45
H2O
(wt%) 2.554 2.680 2.734 2.556 2.654 2.760 2.559 2.627 2.421 2.524
Range in
% PEC* 3.1- 12.3
(ppm)
Li 8.85 11.27 11.34 11.48 9.33 15.27 12.72 10.35 10.66 11.02
B 9.23 7.76 6.41 4.95 5.61 6.41 6.53 5.68 6.17 7.20
P 1050 1123 1064 1068 1043 1732 1622 1160 1371 1856
Ti 4998 4777 4833 4701 4903 5972 6069 5802 5745 6153
V 214 220 204 239 218 236 224 191 208 260
Cu 75 91 84 82 77 86 97 69 72 95
Rb 18.16 17.35 18.56 16.91 16.23 23.04 19.94 16.86 16.87 19.40
Sr 376 344 383 355 357 419 431 424 412 405
Y 11.92 15.21 13.50 13.36 13.60 16.51 15.35 14.43 16.16 15.86
Zr 78.80 76.91 75.64 69.07 74.46 96.86 94.69 95.01 98.97 91.08
Nb 4.24 4.01 4.43 4.01 4.12 6.46 6.99 6.05 6.44 6.40
Ba 234 204 242 203 219 271 265 268 269 248
La 7.59 7.59 7.67 7.23 7.57 10.30 10.07 10.47 10.42 9.94
Ce 18.26 18.04 18.74 18.43 17.72 26.03 22.62 22.94 23.80 27.27
Pr 2.49 2.35 2.30 2.20 2.27 2.88 3.05 2.85 3.14 3.09
Nd 11.01 10.44 10.46 9.94 9.60 13.45 12.91 13.46 13.84 11.42
Sm 2.48 2.84 2.17 1.99 2.46 2.55 2.99 3.06 2.86 2.18
Eu 0.84 0.66 0.77 0.72 1.02 0.72 0.95 1.05 1.01 0.98
Gd 3.00 2.62 2.42 2.49 1.76 2.79 2.73 3.56 1.93 2.64
Dy 2.60 2.44 2.62 2.67 2.44 2.47 2.73 3.18 2.90 2.75
Er 1.56 1.78 1.26 1.95 1.40 2.12 1.83 2.09 1.82 1.89
Yb 1.40 1.34 1.58 1.55 1.68 2.11 1.40 2.57 1.50 1.72
Hf 1.91 1.86 2.09 1.61 1.93 2.24 1.99 2.12 2.41 2.05
Ta 0.12 0.25 0.17 0.19 0.22 0.28 0.41 0.39 0.46 0.30
Pb 3.65 3.54 3.72 2.87 3.15 3.80 3.92 3.36 3.89 6.31
Th 1.86 1.56 1.90 1.36 1.29 1.76 1.89 1.80 2.06 1.51
U 0.49 0.47 0.59 0.37 0.47 0.56 0.57 0.46 0.61 0.83
117
BRVB BRVB-
S-14
BRVB-
S-11
BRVB-
S-9
BRVB-
S-8
BRVB-
S-13
BRVB-
S-6
BRVB-
S-1
δD (‰) -42.09 46.15 8.06 -23.27 4.63 162.27 82.13
H2O
(wt%) 2.187 1.632 1.922 2.236 1.918 0.542 1.372
Range in
% PEC* 3.1-10.2
(ppm)
Li 6.90 10.48 13.58 9.72 7.14 7.00 8.41
B 4.49 5.46 7.06 4.02 3.61 4.47 4.97
P 1891 1946 2269 1436 1566 1541 1623
Ti 7375 7300 7474 7241 7592 7072 7378
V 216 251 246 208 209 210 203
Cu 65 78 75 60 66 42 61
Rb 18.05 19.01 21.63 14.82 16.26 15.24 16.75
Sr 427 417 391 432 427 398 420
Y 17.15 18.04 19.67 18.14 17.18 19.37 18.24
Zr 96.59 96.99 109.14 110.82 105.87 94.69 104.66
Nb 6.61 6.78 7.04 5.98 6.45 6.08 6.30
Ba 337 335 327 361 350 311 333
La 12.91 12.22 13.79 13.46 13.79 12.79 13.08
Ce 29.56 29.42 32.24 32.64 32.20 27.83 29.09
Pr 3.51 3.71 3.77 3.96 3.91 3.88 4.08
Nd 17.23 16.13 18.26 20.70 17.47 16.12 16.80
Sm 4.05 4.04 3.55 4.47 3.63 4.08 3.80
Eu 1.26 1.19 1.14 1.43 0.92 1.19 1.16
Gd 3.66 3.50 4.30 3.68 4.05 3.43 3.56
Dy 3.34 3.24 3.68 4.20 3.61 3.76 3.52
Er 2.21 1.72 2.05 2.27 1.78 2.13 1.90
Yb 1.60 1.86 1.92 2.20 1.54 2.03 1.56
Hf 2.40 2.22 2.26 3.04 2.18 2.30 2.19
Ta 0.40 0.33 0.27 0.32 0.33 0.31 0.33
Pb 3.89 3.76 4.54 4.06 4.14 3.05 3.24
Th 1.31 1.55 1.71 2.07 1.66 1.34 1.62
U 0.49 0.56 0.40 0.40 0.53 0.41 0.51
118
BPPC BPPC-
S-01
BPPC-
S-07
BPPC-
S-11
BPPC-
S-05
BPPC-
S-04
δD (‰) -47.21 -35.26 -45.98 -56.15 -46.61
H2O
(wt%) 2.127 2.161 2.154 2.194 2.206
Range in
% PEC* 0.3-12
(ppm)
Li 6.28 7.97 9.33 5.27 7.81
B 1.79 2.80 4.77 2.40 3.82
P 762 738 746 694 744
Ti 4602 4993 4929 4775 5100
V 246 279 231 232 249
Cu 296 14 28 38 32
Rb 4.49 7.14 6.00 5.89 6.94
Sr 451 470 469 448 455
Y 13.86 16.00 16.60 15.42 15.22
Zr 51.76 61.96 64.83 57.14 60.58
Nb 1.06 1.59 1.74 1.45 2.02
Ba 97 128 125 117 131
La 4.72 5.58 5.86 5.42 5.58
Ce 13.03 14.96 15.25 13.72 15.47
Pr 1.82 1.80 2.12 2.02 1.95
Nd 8.72 10.91 9.55 8.14 9.15
Sm 1.55 2.20 2.50 2.85 2.14
Eu 0.84 0.90 1.08 0.88 0.84
Gd 2.40 2.20 3.16 3.26 2.88
Dy 3.01 3.19 3.69 2.18 2.43
Er 1.74 2.30 2.37 1.95 1.44
Yb 1.40 1.32 1.72 1.66 1.69
Hf 1.50 1.10 1.42 1.56 1.35
Ta N/A N/A 0.07 0.10 0.14
Pb 3.22 3.40 2.04 2.07 2.65
Th 0.37 0.68 0.64 0.52 0.58
U 0.17 0.19 0.13 0.16 0.16
119
BAS-44-
S-03
BAS-44-
S-01
BAS-44-
S-06
BPB-S-
02
BPB-S-
04
BPB-S-
07
BPB-S-
08
δD (‰) -52.65 -52.37 -29.73 -25.14 -29.12 -37.31 -34.92
H2O
(wt%) 1.135 1.169 0.863 2.299 2.485 2.576 2.506
Range in 1.8-4.3 (BAS-44)
0.1-12 (BPB)
% PEC*
(ppm)
Li 5.13 6.33 3.25 8.67 10.05 9.97 11.06
B 3.01 6.24 2.52 6.42 9.13 4.57 16.96
P 1127 949 1091 2017 1536 1356 1897
Ti 6353 6104 6185 6720 5218 5218 5328
V 229 223 232 255 230 212 256
Cu 50 127 133 97 84 77 100
Rb 5.03 3.76 6.20 16.46 16.38 12.96 25.72
Sr 440 389 416 420 450 450 465
Y 19.18 19.14 19.78 16.14 13.39 14.15 14.47
Zr 78.63 78.49 77.06 96.31 90.32 80.91 83.56
Nb 3.21 3.38 3.16 7.93 5.12 5.28 5.30
Ba 124 126 145 362 314 316 316
La 7.18 7.36 7.66 12.83 11.42 10.84 10.42
Ce 21.35 23.03 21.03 28.91 26.99 25.48 25.74
Pr 2.87 3.13 2.95 3.71 3.23 3.29 3.44
Nd 13.50 13.26 12.72 15.62 14.31 12.72 13.45
Sm 3.36 2.75 3.12 2.98 3.20 2.47 3.68
Eu 1.26 1.00 0.89 1.11 0.93 0.78 0.89
Gd 2.86 3.68 2.57 3.06 2.77 2.70 2.38
Dy 3.71 3.11 3.84 3.00 2.31 3.64 2.30
Er 2.59 2.47 2.42 1.44 1.49 1.86 1.49
Yb 1.64 1.09 2.09 0.84 1.76 1.41 1.37
Hf 1.57 1.78 1.69 2.95 2.30 2.29 1.91
Ta N/A N/A 0.25 0.25 0.33 0.26 0.30
Pb 1.92 1.59 2.93 4.31 5.25 3.70 6.15
Th 0.55 0.40 0.83 1.37 1.52 1.43 1.70
U 0.16 0.23 0.28 0.53 0.81 0.45 0.85
120
Average Error
NanoSIMS
δD (‰) ±12‰ (2σ)
H2O (wt%) 0.12 wt% (2σ)
LA-ICP-MS
(ppm) 1 S.E.
Li 0.94
B 0.89
P 73
Ti 139
V 7.22
Cu 6.46
Rb 0.63
Sr 8.67
Y 0.53
Zr 2.41
Nb 0.26
Ba 4.9
La 0.35
Ce 0.63
Pr 0.15
Nd 0.64
Sm 0.32
Eu 0.11
Gd 0.38
Dy 0.28
Er 0.24
Yb 0.27
Hf 0.27
Ta 0.09
Pb 0.39
Th 0.15
U 0.16
121
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125
APPENDIX B
CHAPTER III SUPPLEMENTARY MATERIALS
B.1. Restored Melt Inclusion Compositions
Data in this table represents individual melt inclusion compositions that have been
corrected for Fe loss and post-entrapment crystallization (PEC). Major elements were
restored using Petrolog 3.1.1 (Danyushevsky and Plechov, 2011). Volatile and trace
elements were restored by the same percent as K2O because all are incompatible in the
olivine host. Major element standard deviations represent an average of those calculated
for each melt inclusion from a given sample based on three EPMA point analyses. Trace
element standard deviations are also an average from individual inclusions from a given
sample based on the methods of Loewen and Kent (2012).
126
SAMPLE BBL BBL BBL BBL BBL BBL BBL BBL BBL BBL BBL
avg
s.d.
INC # 1 3 4 6 8 9 13 15 18 20 21
wt%
SiO2 49.89 49.09 48.35 49.33 50.74 48.85 48.30 49.88 49.09 49.79 49.09 0.11
TiO2 1.22 0.96 0.82 1.09 1.27 0.99 0.88 1.26 1.05 1.07 1.01 0.03
Al2O3 16.85 17.29 16.64 16.90 15.77 17.53 17.42 16.66 17.22 16.43 16.97 0.15
FeOT 9.42 9.42 9.42 9.42 9.42 9.42 9.42 9.42 9.42 9.42 9.42 0.11
MnO 0.16 0.15 0.09 0.15 0.17 0.13 0.12 0.15 0.14 0.14 0.13 0.01
MgO 7.20 8.15 10.05 7.74 6.84 7.86 9.06 7.27 7.60 8.05 8.48 0.06
CaO 10.30 10.61 10.86 10.35 9.54 10.40 10.14 9.05 10.06 10.01 9.89 0.03
Na2O 3.17 2.96 2.54 3.11 3.51 3.18 2.90 3.50 3.20 3.19 3.09 0.02
K2O 0.46 0.30 0.15 0.39 0.71 0.37 0.28 0.72 0.41 0.39 0.37 0.01
P2O5 0.21 0.15 0.10 0.18 0.27 0.17 0.15 0.29 0.19 0.18 0.16 0.01
S 0.11 0.11 0.08 0.11 0.12 0.11 0.10 0.12 0.12 0.11 0.11 0.003
Cl 0.024 0.014 0.010 0.017 0.024 0.023 0.011 0.025 0.017 0.022 0.015 0.004
CO2
(ppm) 897 784 437 848 929 866 549 1034 852 712 856 69
H2O 0.94 0.77 0.80 1.17 1.47 0.94 1.18 1.57 1.47 1.15 1.23 0.06
% PEC 1.20 4.54 14.39 2.38 0.60 2.40 7.81 1.80 1.31 3.87 6.36
Fo 83.7 85.3 87.8 84.7 83.0 85.0 86.7 84.0 84.5 85.2 85.9
ppm
Li N/A N/A 8.92 7.78 9.18 7.41 7.78 9.38 5.96 8.05 6.07 1.50
B N/A N/A 3.27 1.87 5.16 0.47 2.63 3.59 1.82 2.42 1.38 1.13
Sc N/A N/A 45.14 40.10 40.70 36.03 33.19 42.02 41.90 38.61 37.65 3.33
V N/A N/A 248 236 266 221 209 219 226 234 226 13
Rb N/A N/A 2.06 5.67 9.74 5.21 4.06 8.16 6.11 6.52 5.40 0.31
Sr N/A N/A 193 275 308 270 249 307 285 269 275 5
Y N/A N/A 19.41 21.35 24.52 20.05 19.09 24.86 23.85 21.60 21.25 1.73
Zr N/A N/A 56.34 78.59 118.55 73.80 70.39 106.75 92.64 79.53 81.12 6.63
Nb N/A N/A 1.08 2.97 5.41 2.92 2.70 4.96 3.41 3.23 2.73 0.35
Ba N/A N/A 70.06 170.44 297.04 147.14 122.48 247.66 174.24 168.02 154.92 4.36
La N/A N/A 2.94 6.44 10.98 5.81 4.92 10.44 7.55 6.62 6.10 0.19
Ce N/A N/A 8.81 16.81 29.05 14.96 13.12 25.37 17.57 16.95 15.93 0.43
Pr N/A N/A 1.26 2.37 3.85 2.04 1.88 3.40 2.54 2.33 2.04 0.10
Nd N/A N/A 6.77 11.83 17.27 10.93 9.02 15.23 11.62 11.07 10.35 0.32
Sm N/A N/A 2.37 2.93 4.24 2.51 2.53 3.59 2.72 3.02 2.94 0.14
Eu N/A N/A 0.83 1.09 1.43 0.98 0.98 1.22 1.03 1.17 1.00 0.08
Gd N/A N/A 3.45 3.59 3.87 3.29 2.92 4.47 4.36 3.62 3.24 0.19
Dy N/A N/A 3.29 3.74 4.66 3.91 3.53 4.08 4.14 3.83 3.68 0.15
Er N/A N/A 2.41 2.47 2.73 2.38 2.17 3.18 2.85 2.74 2.47 0.14
Yb N/A N/A 2.45 2.44 2.84 2.24 2.42 3.07 2.47 2.60 2.67 0.15
Hf N/A N/A 1.36 1.95 2.58 1.55 1.50 2.57 1.96 2.09 1.61 0.11
Ta N/A N/A 0.06 0.17 0.36 0.13 0.15 0.29 0.19 0.18 0.19 0.03
Pb N/A N/A 0.89 2.15 3.65 1.70 1.46 3.13 2.08 2.01 1.70 0.11
Th N/A N/A 0.18 0.59 0.99 0.57 0.33 0.89 0.55 0.56 0.49 0.05
U N/A N/A 0.08 0.23 0.39 0.15 0.13 0.34 0.18 0.20 0.17 0.02
127
BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB BPB
avg
s.d.
INC # 1 3a 3b 4 5 9 10a 10b 14a 14b 17 18 19 20 21 22
wt%
SiO2 50.77 51.21 51.27 50.14 50.44 51.45 50.98 50.39 51.42 52.17 51.42 50.83 49.88 51.26 51.07 51.16 0.24
TiO2 0.90 0.90 0.91 0.86 0.88 0.90 0.87 0.88 0.87 0.85 0.92 0.89 0.85 0.93 0.96 0.87 0.01
Al2O3 17.19 17.07 17.20 16.67 17.73 17.01 15.86 16.68 16.18 15.88 17.16 16.65 17.64 16.98 18.27 16.63 0.07
FeOT 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 7.65 0.07
MnO 0.12 0.12 0.12 0.11 0.11 0.12 0.09 0.11 0.10 0.13 0.15 0.12 0.11 0.16 0.11 0.09 0.01
MgO 7.07 6.85 6.84 7.88 7.46 6.84 7.91 7.90 7.77 7.73 7.73 7.83 7.69 7.38 6.14 7.29 0.18
CaO 10.37 10.05 10.13 9.67 9.89 10.21 10.02 10.38 9.96 9.77 10.40 10.00 10.13 10.25 10.08 10.12 0.10
Na2O 2.61 2.83 2.80 2.91 2.91 2.87 2.93 2.82 2.73 2.88 2.71 2.60 2.55 3.22 2.86 3.08 0.06
K2O 0.77 0.82 0.84 0.81 0.76 0.82 0.75 0.75 0.76 0.82 1.01 0.80 0.78 1.02 0.87 0.78 0.02
P2O 0.25 0.24 0.23 0.24 0.24 0.27 0.24 0.24 0.24 0.23 0.25 0.24 0.25 0.25 0.26 0.25 0.01
S 0.11 0.09 0.09 0.11 0.11 0.09 0.12 0.11 0.11 0.09 0.06 0.12 0.11 0.09 0.09 0.11 0.003
Cl 0.060 0.061 0.061 0.058 0.050 0.059 0.063 0.057 0.058 0.059 0.059 0.058 0.059 0.069 0.061 0.058 0.001
CO2
(ppm) 629 370 285 847 581 310 1563 1061 1123 475 135 412 1385 106 231 660 83
H2O 2.42 2.37 2.12 3.18 2.04 1.99 2.81 2.34 2.45 2.00 0.72 2.51 2.58 0.96 1.85 2.20 0.16
%
PEC 2.66 0.55 0.00 2.93 2.24 3.67 10.70 6.78 4.79 3.23 3.61 3.93 4.18 2.69 0.19 4.09
Fo 86.1 85.8 85.8 87.7 87.0 85.8 87.7 87.7 87.3 87.3 87.4 87.4 87.2 87.1 84.4 86.8
ppm
Li 8.63 8.49 N/A 7.21 4.54 8.17 15.49 14.52 8.12 10.36 10.73 N/A N/A 12.39 N/A 8.82 1.97
B 4.97 10.13 N/A 17.00 3.09 8.71 5.50 5.34 4.70 7.52 9.85 N/A N/A 6.63 N/A 11.88 1.68
Sc 34.01 35.74 N/A 35.39 34.32 36.58 53.90 41.41 38.30 28.17 38.40 N/A N/A 38.90 N/A 36.59 1.51
V 244 207 N/A 217 171 212 318 254 227 217 227 N/A N/A 263 N/A 226 11
Rb 15.22 16.97 N/A 17.14 11.37 14.87 18.36 14.47 14.90 15.57 18.53 N/A N/A 21.09 N/A 13.95 0.95
Sr 531 446 N/A 499 481 481 510 523 498 466 476 N/A N/A 452 N/A 551 7
Y 19.08 16.31 N/A 17.45 16.55 15.69 17.24 16.13 15.41 13.99 17.71 N/A N/A 18.47 N/A 15.60 0.76
Zr 108 90 N/A 102 96 92 107 96 97 101 106 N/A N/A 106 N/A 95 4
Nb 6.48 5.54 N/A 5.97 5.37 5.66 5.80 5.22 5.47 5.44 6.11 N/A N/A 6.88 N/A 6.28 0.36
Ba 328 304 N/A 336 258 308 359 338 304 311 374 N/A N/A 401 N/A 319 5
La 13.71 10.27 N/A 12.72 11.59 11.54 11.77 11.52 10.52 11.99 12.75 N/A N/A 13.38 N/A 12.23 0.21
Ce 28.33 22.96 N/A 23.35 20.34 25.62 35.87 29.11 25.95 25.69 28.74 N/A N/A 30.62 N/A 29.65 0.55
Pr 4.06 3.36 N/A 3.77 3.14 2.96 4.05 3.01 3.40 3.22 3.40 N/A N/A 4.02 N/A 3.54 0.15
Nd 14.55 15.10 N/A 15.95 11.24 13.80 15.26 18.17 13.45 13.35 17.43 N/A N/A 18.56 N/A 16.10 0.57
Sm 3.59 3.89 N/A 3.38 3.04 3.47 2.42 2.37 2.45 3.94 3.81 N/A N/A 3.60 N/A 3.07 0.33
Eu 1.20 1.03 N/A 1.15 1.14 1.02 1.09 1.02 1.01 0.95 1.10 N/A N/A 1.19 N/A 1.14 0.09
Gd 3.80 3.60 N/A 3.30 2.91 2.80 2.68 3.90 3.22 3.41 3.02 N/A N/A 4.82 N/A 3.29 0.18
Dy 3.18 3.20 N/A 3.09 2.30 2.92 3.38 3.30 3.12 2.52 2.85 N/A N/A 3.70 N/A 3.26 0.19
Er 1.69 1.61 N/A 1.73 1.91 2.43 1.68 1.46 1.84 3.26 1.91 N/A N/A 1.86 N/A 1.99 0.07
Yb 2.02 2.06 N/A 1.64 1.50 2.41 1.89 1.69 1.18 1.63 1.75 N/A N/A 1.77 N/A 1.85 0.14
Hf 2.69 2.45 N/A 2.24 3.38 2.64 2.36 2.36 1.16 2.41 3.09 N/A N/A 2.79 N/A 1.70 0.15
Ta 0.33 0.40 N/A 0.37 0.33 0.33 0.32 0.28 0.47 0.27 0.32 N/A N/A 0.39 N/A 0.24 0.03
Pb 4.29 4.73 N/A 4.46 2.92 4.65 4.76 4.43 4.51 3.33 5.30 N/A N/A 5.97 N/A 3.81 0.21
Th 2.78 1.93 N/A 1.57 1.53 2.08 1.59 1.60 1.34 1.91 1.99 N/A N/A 2.03 N/A 1.60 0.13
U 0.61 0.55 N/A 0.40 0.39 0.52 0.53 0.54 0.52 0.64 0.63 N/A N/A 0.70 N/A 0.64 0.06
128
BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM BRM
avg
s.d.
INC # 1 2 3 5 6 7 8 9 10 11 14a 14b 15 16 18
wt%
SiO2 49.33 50.01 50.93 49.72 52.70 49.58 48.74 49.63 48.55 50.89 50.28 50.39 49.99 49.72 50.22 0.29
TiO2 0.85 0.88 0.80 0.86 0.89 0.87 0.93 0.80 0.82 0.82 0.91 0.91 0.92 0.94 0.87 0.01
Al2O3 18.74 20.14 18.15 17.32 15.05 17.86 17.64 17.58 17.87 18.93 19.82 19.87 18.19 17.75 19.11 0.22
FeOT 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 8.14 0.06
MnO 0.09 0.11 0.12 0.09 0.09 0.10 0.09 0.09 0.08 0.12 0.12 0.12 0.08 0.06 0.11 0.01
MgO 7.31 5.61 5.90 7.59 7.68 7.73 7.26 7.72 7.87 5.70 5.59 5.58 7.40 8.46 5.72 0.28
CaO 9.73 8.92 8.38 9.43 7.65 9.95 9.64 9.74 9.68 8.82 8.61 8.63 9.73 9.71 8.23 0.14
Na2O 4.12 4.26 3.89 3.55 3.45 3.46 3.87 3.85 3.75 3.89 4.06 4.07 3.86 3.43 3.90 0.15
K2O 0.70 0.83 0.79 0.75 0.91 0.72 0.78 0.64 0.71 0.80 0.75 0.75 0.73 0.86 0.75 0.02
P2O5 0.31 0.31 0.28 0.32 0.32 0.30 0.34 0.27 0.28 0.27 0.25 0.25 0.28 0.31 0.24 0.02
S 0.20 0.17 0.17 0.20 0.08 0.21 0.21 0.22 0.23 0.16 0.16 0.16 0.20 0.21 0.16 0.001
Cl 0.24 0.22 0.21 0.20 0.18 0.23 0.21 0.25 0.25 0.21 0.23 0.23 0.25 0.24 0.23 0.001
CO2
(ppm) 0 0 166 193 378 321 599 251 306 141 0 0 0 0 270 20
H2O 0.49 0.57 2.36 2.03 2.97 1.14 2.43 1.39 2.11 1.43 1.35 1.14 0.53 0.45 2.57 0.08
% PEC 8.13 2.19 1.20 10.26 8.42 7.48 7.21 8.10 8.15 2.11 3.79 3.72 9.26 12.75 1.23
Fo 86.5 82.8 83.0 86.5 86.4 86.8 86.4 87.0 87.3 82.6 82.6 82.6 86.5 87.9 82.8
ppm
Li 5.33 N/A 11.50 6.27 11.71 N/A N/A N/A N/A 4.51 N/A N/A 4.86 N/A 6.68 1.22
B 3.02 N/A 2.74 4.65 2.74 N/A N/A N/A N/A 2.18 N/A N/A 3.71 N/A 3.22 2.30
Sc 25.93 N/A 22.28 26.34 24.27 N/A N/A N/A N/A 20.18 N/A N/A 22.34 N/A 19.55 2.11
V 223 N/A 181 202 205 N/A N/A N/A N/A 168 N/A N/A 219 N/A 154 8
Rb 7.30 N/A 11.75 9.97 13.74 N/A N/A N/A N/A 10.24 N/A N/A 8.81 N/A 11.19 0.46
Sr 1378 N/A 1173 1257 969 N/A N/A N/A N/A 1039 N/A N/A 1395 N/A 1167 7
Y 11.08 N/A 11.44 11.39 12.27 N/A N/A N/A N/A 9.42 N/A N/A 11.72 N/A 12.25 0.83
Zr 85.70 N/A 92.69 92.57 98.34 N/A N/A N/A N/A 79.07 N/A N/A 95.32 N/A 84.94 5.05
Nb 3.96 N/A 4.58 5.14 6.73 N/A N/A N/A N/A 6.63 N/A N/A 5.26 N/A 4.25 0.49
Ba 236 N/A 283 285 332 N/A N/A N/A N/A 263 N/A N/A 284 N/A 257 8
La 14.62 N/A 14.98 15.78 16.43 N/A N/A N/A N/A 13.53 N/A N/A 16.02 N/A 13.95 0.25
Ce 35.41 N/A 36.69 37.51 37.32 N/A N/A N/A N/A 32.29 N/A N/A 37.74 N/A 31.52 0.51
Pr 4.20 N/A 4.27 4.41 4.71 N/A N/A N/A N/A 4.09 N/A N/A 4.65 N/A 4.19 0.08
Nd 17.50 N/A 19.52 19.33 20.35 N/A N/A N/A N/A 17.00 N/A N/A 19.73 N/A 17.92 0.30
Sm 3.61 N/A 2.82 3.54 2.98 N/A N/A N/A N/A 3.10 N/A N/A 3.64 N/A 3.42 0.26
Eu 1.11 N/A 1.12 1.14 1.15 N/A N/A N/A N/A 1.09 N/A N/A 1.30 N/A 0.95 0.06
Gd 2.97 N/A 2.88 2.75 2.49 N/A N/A N/A N/A 2.87 N/A N/A 3.06 N/A 2.97 0.07
Dy 2.36 N/A 1.96 2.45 2.07 N/A N/A N/A N/A 1.54 N/A N/A 2.40 N/A 2.00 0.13
Er 1.44 N/A 1.31 1.39 1.16 N/A N/A N/A N/A 0.64 N/A N/A 1.36 N/A 1.39 0.16
Yb 1.34 N/A 1.27 1.77 1.11 N/A N/A N/A N/A 0.71 N/A N/A 1.23 N/A 1.44 0.20
Hf 2.03 N/A 2.78 2.35 2.32 N/A N/A N/A N/A 1.69 N/A N/A 2.58 N/A 2.54 0.12
Ta 0.17 N/A 0.22 0.24 0.29 N/A N/A N/A N/A 0.27 N/A N/A 0.23 N/A 0.18 0.04
Pb 4.57 N/A 5.08 5.08 5.80 N/A N/A N/A N/A 4.15 N/A N/A 4.39 N/A 4.63 0.17
Th 1.30 N/A 1.94 1.75 1.82 N/A N/A N/A N/A 1.46 N/A N/A 1.68 N/A 1.82 0.11
U 0.46 N/A 0.47 0.47 0.60 N/A N/A N/A N/A 0.38 N/A N/A 0.51 N/A 0.51 0.04
129
BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB BRVB s.d.
INC# 1 3 4 5 6 8 9 10 11 13 18 20 21 22
wt%
SiO2 48.76 49.64 49.12 49.26 49.05 49.23 53.11 49.47 48.35 49.67 49.08 50.96 48.27 48.49 0.17
TiO2 1.29 1.47 1.36 1.34 1.34 1.45 2.37 1.36 1.35 1.31 1.33 1.42 1.44 1.32 0.03
Al2O3 17.81 15.97 16.28 17.50 16.42 16.92 14.18 15.51 16.57 15.78 16.95 15.41 18.48 16.43 0.08
FeOT 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 0.06
MnO 0.12 0.13 0.13 0.14 0.14 0.14 0.13 0.14 0.13 0.15 0.14 0.12 0.14 0.15 0.01
MgO 7.44 7.35 7.52 7.28 7.45 6.95 6.99 7.15 7.19 8.09 7.21 7.26 6.67 7.28 0.03
CaO 8.67 9.25 9.59 9.46 9.80 9.85 7.99 9.64 9.24 9.59 9.46 9.37 9.91 9.35 0.03
Na2O 3.75 3.27 3.31 3.38 3.32 3.77 2.91 3.27 3.60 3.54 3.49 3.34 3.67 3.24 0.07
K2O 1.25 1.02 1.01 1.05 0.96 1.13 1.66 0.98 1.04 0.93 0.94 1.18 1.13 0.95 0.02
P2O5 0.30 0.32 0.29 0.32 0.29 0.35 0.51 0.30 0.28 0.26 0.29 0.27 0.33 0.28 0.01
S 0.14 0.19 0.16 0.19 0.20 0.17 0.01 0.20 0.19 0.17 0.17 0.04 0.16 0.20 0.002
Cl 0.038 0.048 0.049 0.049 0.049 0.049 0.056 0.050 0.049 0.039 0.039 0.038 0.049 0.04 0.002
CO2
(ppm) 657 748 595 644 0 287 403 410 619 419 551 455 123 560 34
H2O 1.00 2.01 1.82 0.71 1.68 0.63 0.57 2.61 2.70 1.12 1.57 1.07 0.38 2.89 0.10
% PEC 6.85 6.87 4.79 3.55 3.87 3.16 6.53 2.01 2.57 4.77 2.88 7.67 3.23 2.78
Fo 85.0 84.4 84.8 84.4 84.7 84.2 83.5 84.0 84.5 85.9 84.3 84.2 83.6 84.2
ppm
Li N/A 10.77 10.13 N/A 10.19 N/A N/A 12.11 9.86 N/A 16.23 N/A 0.26 10.88 1.70
B N/A 6.17 16.19 N/A 5.28 N/A N/A 114.73 4.86 N/A 11.14 N/A 10.81 4.25 2.80
Sc N/A 36.50 30.06 N/A 31.16 N/A N/A 33.44 29.58 N/A 37.74 N/A 48.40 27.67 1.43
V N/A 262 230 N/A 249 N/A N/A 235 239 N/A 310 N/A 408 240 13
Rb N/A 21.73 18.91 N/A 19.68 N/A N/A 26.62 18.56 N/A 25.51 N/A 32.25 19.88 0.53
Sr N/A 456 457 N/A 453 N/A N/A 454 437 N/A 469 N/A 326 455 7
Y N/A 18.88 18.69 N/A 18.69 N/A N/A 17.31 17.81 N/A 19.29 N/A 33.83 17.25 0.74
Zr N/A 110 107 N/A 103 N/A N/A 102 99 N/A 112 N/A 200 99 5
Nb N/A 6.77 6.77 N/A 6.66 N/A N/A 7.43 6.77 N/A 7.63 N/A 11.80 6.91 0.33
Ba N/A 412 359 N/A 361 N/A N/A 386 347 N/A 425 N/A 548 366 7
La N/A 14.20 13.56 N/A 14.08 N/A N/A 13.98 13.20 N/A 16.37 N/A 23.82 13.67 0.22
Ce N/A 35.99 32.43 N/A 32.93 N/A N/A 33.25 32.71 N/A 43.15 N/A 51.57 33.63 0.70
Pr N/A 4.45 4.23 N/A 4.16 N/A N/A 4.32 4.07 N/A 5.15 N/A 7.43 4.22 0.10
Nd N/A 20.63 18.70 N/A 18.95 N/A N/A 20.17 18.27 N/A 20.61 N/A 34.49 20.31 0.43
Sm N/A 4.23 4.35 N/A 4.00 N/A N/A 4.38 4.00 N/A 4.67 N/A 7.10 4.16 0.13
Eu N/A 1.40 1.31 N/A 1.36 N/A N/A 1.31 1.38 N/A 1.45 N/A 1.99 1.25 0.08
Gd N/A 3.97 3.92 N/A 3.91 N/A N/A 3.88 3.73 N/A 4.68 N/A 6.88 3.61 0.21
Dy N/A 3.53 3.60 N/A 3.46 N/A N/A 3.57 3.37 N/A 4.28 N/A 6.02 3.82 0.20
Er N/A 2.12 1.91 N/A 2.05 N/A N/A 1.85 1.94 N/A 2.13 N/A 3.55 1.79 0.08
Yb N/A 2.00 1.67 N/A 1.92 N/A N/A 1.65 1.73 N/A 2.78 N/A 3.21 1.70 0.05
Hf N/A 2.69 2.56 N/A 2.74 N/A N/A 2.38 2.31 N/A 2.59 N/A 4.36 2.51 0.13
Ta N/A 0.38 0.38 N/A 0.32 N/A N/A 0.34 0.29 N/A 0.42 N/A 0.67 0.34 0.06
Pb N/A 4.11 3.85 N/A 3.84 N/A N/A 3.92 3.79 N/A 5.32 N/A 6.75 4.15 0.18
Th N/A 1.77 1.61 N/A 1.76 N/A N/A 1.73 1.70 N/A 1.99 N/A 2.67 1.80 0.12
U N/A 0.61 0.54 N/A 0.63 N/A N/A 0.63 0.61 N/A 0.65 N/A 1.00 0.62 0.05
130
BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC BPPC s.d.
INC# 1 2 3 5 7 10 11 12 13 15 17a 17b 18 19
wt%
SiO2 50.52 50.21 50.13 49.64 50.62 50.17 50.27 50.68 51.03 51.55 50.39 50.31 50.22 50.44 0.29
TiO2 0.78 0.78 0.71 0.76 0.80 0.79 0.77 0.81 0.76 1.01 0.80 0.80 0.82 0.77 0.02
Al2O3 16.42 16.52 16.65 16.64 16.47 16.48 16.56 16.47 15.38 15.59 16.24 16.76 16.72 16.72 0.13
FeOT 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 7.68 0.07
MnO 0.13 0.11 0.10 0.12 0.12 0.11 0.13 0.11 0.13 0.18 0.11 0.12 0.14 0.14 0.01
MgO 7.88 8.40 8.43 8.26 7.98 8.04 8.06 8.13 7.55 8.20 8.15 8.19 7.75 7.75 0.18
CaO 10.79 10.71 11.06 11.52 10.77 11.01 10.77 10.89 11.34 11.34 10.93 10.69 11.12 10.89 0.10
Na2O 2.71 2.68 2.58 2.38 2.73 2.69 2.67 2.82 2.63 3.04 2.77 2.71 2.85 2.80 0.11
K2O 0.31 0.30 0.24 0.19 0.33 0.31 0.35 0.32 0.30 0.45 0.31 0.30 0.36 0.31 0.02
P2O5 0.18 0.17 0.18 0.16 0.19 0.19 0.19 0.18 0.21 0.22 0.19 0.18 0.19 0.18 0.01
S 0.12 0.11 0.11 0.13 0.12 0.12 0.12 0.12 0.12 0.07 0.11 0.11 0.13 0.11 0.003
Cl 0.039 0.039 0.037 0.040 0.040 0.039 0.040 0.039 0.030 0.050 0.039 0.038 0.040 0.040 0.001
CO2
(ppm) 908 878 954 758 1300 1008 1012 672 892 85 876 1011 954 735 52
H2O 2.50 2.32 2.12 2.54 2.19 2.43 2.44 1.79 2.85 0.61 2.32 2.15 2.05 2.21 0.11
% PEC 1.48 3.37 9.49 1.47 0.82 2.59 1.13 5.00 1.79 1.26 3.17 4.40 0.82 0.87
Fo 87 88 88 88 87 87 87 88 86 88 88 88 87 87
ppm
Li 6.14 6.06 6.89 N/A N/A 5.80 7.25 N/A 4.00 6.99 7.35 N/A 7.04 N/A 1.36
B 1.74 2.69 1.31 N/A N/A 1.32 2.30 N/A 4.61 3.43 N/A N/A 4.34 N/A 1.77
Sc 35.87 34.04 31.48 N/A N/A 33.30 33.74 N/A 35.34 40.37 36.71 N/A 36.15 N/A 1.45
V 211 212 215 N/A N/A 211 208 N/A 209 238 210 N/A 210 N/A 13
Rb 5.09 4.58 2.72 N/A N/A 4.46 4.95 N/A 5.50 6.75 4.74 N/A 6.16 N/A 0.50
Sr 455 447 345 N/A N/A 456 432 N/A 458 378 445 N/A 455 N/A 6
Y 14.99 15.36 13.39 N/A N/A 16.18 15.15 N/A 15.88 18.39 16.19 N/A 16.12 N/A 0.78
Zr 58.30 60.60 41.62 N/A N/A 54.75 58.19 N/A 58.42 68.02 59.08 N/A 61.90 N/A 3.93
Nb 1.41 1.42 0.83 N/A N/A 1.39 1.37 N/A 1.30 1.71 1.40 N/A 1.65 N/A 0.34
Ba 111 102 61 N/A N/A 102 105 N/A 119 136 105 N/A 118 N/A 4
La 5.14 5.23 3.79 N/A N/A 5.33 5.60 N/A 5.74 6.29 4.99 N/A 5.61 N/A 0.20
Ce 13.10 12.54 9.59 N/A N/A 12.52 13.01 N/A 12.91 16.22 13.36 N/A 13.57 N/A 0.36
Pr 1.88 1.66 1.23 N/A N/A 1.66 1.70 N/A 1.85 2.00 1.95 N/A 1.92 N/A 0.13
Nd 9.04 8.29 6.11 N/A N/A 8.78 8.74 N/A 8.48 9.52 9.26 N/A 8.53 N/A 0.24
Sm 2.37 2.56 1.87 N/A N/A 2.16 1.96 N/A 2.42 3.00 1.32 N/A 2.85 N/A 0.12
Eu 0.99 0.78 0.65 N/A N/A 0.75 0.83 N/A 0.82 0.85 0.87 N/A 0.92 N/A 0.06
Gd 2.48 2.62 1.77 N/A N/A 2.77 2.64 N/A 3.73 2.42 2.48 N/A 2.68 N/A 0.12
Dy 2.78 2.38 2.27 N/A N/A 2.75 2.73 N/A 2.74 3.16 2.88 N/A 2.43 N/A 0.08
Er 1.57 1.63 1.16 N/A N/A 1.88 1.62 N/A 1.71 1.91 2.47 N/A 1.76 N/A 0.18
Yb 1.70 1.56 1.54 N/A N/A 1.75 1.86 N/A 2.02 1.75 1.62 N/A 1.62 N/A 0.10
Hf 1.66 1.52 1.16 N/A N/A 1.61 1.44 N/A 1.90 1.51 1.95 N/A 1.88 N/A 0.13
Ta 0.09 0.06 N/A N/A N/A 0.05 0.13 N/A 0.04 0.12 0.07 N/A 0.10 N/A 0.03
Pb 1.64 1.56 1.02 N/A N/A 1.50 1.51 N/A 1.96 2.33 1.39 N/A 1.76 N/A 0.18
Th 0.54 0.48 0.30 N/A N/A 0.45 0.60 N/A 0.46 0.69 0.62 N/A 0.60 N/A 0.08
U 0.18 0.17 0.01 N/A N/A 0.16 0.19 N/A 0.25 0.22 0.15 N/A 0.19 N/A 0.03
131
CC CC CC CC CC CC CC CC CC CC CC CC CC
avg
s.d.
INC# 1 2 6 7 9a 9b 4a 4b 10 13 16a 16b 18
wt%
SiO2 51.11 50.20 49.91 50.71 51.11 50.76 50.63 50.88 50.75 52.64 49.96 49.87 50.88 0.34
TiO2 0.87 0.94 0.86 0.83 0.81 0.80 0.85 0.83 0.81 0.81 0.83 0.84 0.83 0.03
Al2O3 16.65 17.98 16.55 16.65 16.27 16.49 16.82 16.59 16.82 16.71 16.47 16.53 16.44 0.27
FeOT 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 6.88 0.13
MnO 0.09 0.09 0.08 0.09 0.09 0.08 0.08 0.09 0.08 0.11 0.10 0.09 0.09 0.01
MgO 7.93 7.47 8.44 8.37 8.38 8.47 7.88 7.95 8.28 7.67 8.25 8.27 8.18 0.75
CaO 10.10 9.42 10.67 10.13 10.15 9.73 10.21 9.90 10.12 8.43 10.68 10.73 10.18 0.22
Na2O 3.24 3.43 2.89 2.77 3.02 2.85 3.17 3.03 3.02 3.52 2.97 2.93 3.07 0.16
K2O 0.86 0.84 0.72 0.82 0.79 0.82 0.81 0.88 0.82 1.27 0.68 0.68 0.79 0.03
P2O5 0.16 0.18 0.16 0.16 0.15 0.15 0.16 0.15 0.16 0.15 0.16 0.15 0.15 0.01
S 0.09 0.09 0.09 0.09 0.09 0.05 0.09 0.09 0.09 0.08 0.09 0.09 0.09 0.003
Cl 0.036 0.038 0.037 0.034 0.040 0.038 0.038 0.035 0.038 0.036 0.037 0.037 0.036 0.003
CO2
(ppm) 922 940 1302 1248 0 789 531 640 1151 612 1431 1464 1266 85
H2O 2.58 3.05 3.33 3.10 2.84 3.46 3.00 3.30 2.74 2.29 3.49 3.52 2.99 0.23
% PEC 6.11 1.70 8.02 0.81 7.49 7.68 6.06 6.76 7.42 6.46 6.05 6.33 6.49
Fo 90 89 90 90 90 90 90 90 90 90 90 90 90
ppm
Li N/A N/A 5.85 9.67 15.71 N/A 7.69 7.20 N/A 8.60 24.63 4.83 N/A 1.23
B N/A N/A 7.20 5.42 6.52 N/A 5.10 2.29 N/A 5.67 9.41 3.83 N/A 2.93
Sc N/A N/A 29.83 30.52 31.25 N/A 26.88 26.93 N/A 25.40 23.61 29.22 N/A 1.36
V N/A N/A 196 206 177 N/A 193 174 N/A 189 162 192 N/A 11
Rb N/A N/A 10.20 17.00 13.96 N/A 13.48 13.65 N/A 12.56 26.23 9.41 N/A 0.71
Sr N/A N/A 347 370 367 N/A 343 346 N/A 325 349 320 N/A 8
Y N/A N/A 15.38 14.10 15.63 N/A 13.02 13.19 N/A 12.48 12.73 13.24 N/A 0.86
Zr N/A N/A 80.98 75.69 89.69 N/A 68.49 71.84 N/A 68.56 73.03 67.73 N/A 4.29
Nb N/A N/A 4.46 4.34 4.05 N/A 3.95 4.04 N/A 3.80 3.90 4.16 N/A 0.33
Ba N/A N/A 178 205 206 N/A 189 198 N/A 182 280 157 N/A 5
La N/A N/A 8.38 7.81 8.05 N/A 7.12 7.54 N/A 6.96 8.77 6.57 N/A 0.47
Ce N/A N/A 17.97 17.59 18.42 N/A 16.72 16.82 N/A 16.13 18.84 15.44 N/A 0.77
Pr N/A N/A 2.50 2.31 2.74 N/A 2.28 2.54 N/A 2.23 2.32 2.17 N/A 0.08
Nd N/A N/A 10.96 10.34 15.03 N/A 10.61 11.35 N/A 10.11 11.53 9.20 N/A 0.37
Sm N/A N/A 2.22 2.61 2.06 N/A 2.30 2.47 N/A 2.51 2.31 2.26 N/A 0.22
Eu N/A N/A 1.03 0.90 1.08 N/A 0.81 0.79 N/A 0.70 0.79 0.79 N/A 0.09
Gd N/A N/A 3.04 2.74 2.87 N/A 2.54 2.75 N/A 2.17 2.33 2.30 N/A 0.24
Dy N/A N/A 2.63 2.56 2.65 N/A 2.30 3.03 N/A 2.58 2.35 2.45 N/A 0.11
Er N/A N/A 1.66 1.38 2.46 N/A 1.40 1.21 N/A 1.29 1.42 1.61 N/A 0.10
Yb N/A N/A 1.43 1.59 1.74 N/A 1.28 1.55 N/A 1.33 1.31 1.30 N/A 0.14
Hf N/A N/A 1.77 1.92 3.45 N/A 1.58 1.91 N/A 1.45 1.82 1.70 N/A 0.15
Ta N/A N/A 0.28 0.25 0.43 N/A 0.24 0.18 N/A 0.38 0.24 0.27 N/A 0.03
Pb N/A N/A 2.40 2.91 2.86 N/A 2.84 2.88 N/A 2.46 6.59 1.66 N/A 0.13
Th N/A N/A 1.29 1.64 1.65 N/A 1.55 1.65 N/A 1.53 2.27 1.12 N/A 0.08
U N/A N/A 0.35 0.51 0.54 N/A 0.46 0.58 N/A 0.46 0.76 0.37 N/A 0.04
132
BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG BORG s.d.
INC # A1 A3 A5 A6 c A9 A10 A18
A20-
2 A23 A24
A24-
2 A28
AA1
c AA4 AA5
wt%
SiO2 47.78 48.41 48.65 49.61 48.20 48.45 49.08 49.31 48.70 48.31 48.46 48.41 49.93 49.15 49.42 0.41
TiO2 0.66 0.67 0.71 0.82 0.64 0.66 0.72 0.80 0.72 0.70 0.68 0.69 0.83 0.85 0.74 0.02
Al2O3 16.95 16.75 16.23 19.21 16.35 17.47 15.72 17.87 16.30 15.89 16.17 17.03 16.88 17.90 15.88 0.28
FeOT 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 8.54 0.11
MnO 0.12 0.11 0.12 0.12 0.11 0.10 0.09 0.13 0.10 0.08 0.10 0.10 0.12 0.12 0.09 0.01
MgO 9.80 9.73 9.51 6.97 9.77 9.69 9.47 7.44 8.99 10.32 10.28 9.67 8.14 7.90 9.34 0.14
CaO 9.76 9.96 9.97 8.73 10.02 9.03 10.13 9.16 10.02 10.73 10.62 10.38 8.76 8.71 9.99 0.11
Na2O 2.63 2.48 2.48 2.46 2.41 2.73 2.41 3.27 2.56 2.36 2.49 2.46 2.74 3.22 2.47 0.14
K2O 0.50 0.47 0.51 0.55 0.49 0.50 0.48 0.52 0.50 0.38 0.40 0.46 0.57 0.54 0.48 0.02
P2O5 0.10 0.07 0.09 0.13 0.07 0.08 0.10 0.10 0.10 0.09 0.09 0.08 0.11 0.11 0.11 0.01
S 0.10 0.11 0.12 0.15 0.12 0.12 0.12 0.11 0.12 0.11 0.12 0.12 0.10 0.21 0.11 0.004
Cl 0.05 0.05 0.05 0.05 0.05 0.06 0.05 0.04 0.05 0.06 0.06 0.05 0.04 0.04 0.05 0.002
CO2
(ppm) 518 853 1114 724 945 887 1493 841 1104 1123 950 793 786 840 984 53
H2O 3.00 2.67 3.07 2.74 3.27 2.62 3.11 2.73 3.34 2.45 2.04 2.04 3.26 2.75 2.80 0.12
PEC 9.80 10.13 9.27 9.25 9.20 19.03 11.61 3.15 13.96 13.95 12.61 14.58 8.99 5.27 12.74
Fo 88.6 88.4 88.2 83.8 88.5 88.4 88.0 85.4 87.5 89.1 89.1 88.4 86.2 86.1 87.9
ppm
Li 7.60 N/A 5.76 N/A 5.43 N/A 10.48 6.51 5.01 6.75 N/A 7.74 6.01 N/A 7.66 1.18
B 2.87 N/A 3.36 N/A 4.41 N/A 3.82 6.91 2.49 4.09 N/A 4.99 3.72 N/A 4.98 1.77
Sc 38.35 N/A 35.93 N/A 37.47 N/A 41.11 29.58 35.29 41.35 N/A 39.69 30.05 N/A 39.37 1.60
V 272 N/A 245 N/A 250 N/A 339 227 236 288 N/A 305 225 N/A 280 16
Rb 5.20 N/A 4.25 N/A 5.95 N/A 6.91 8.83 4.37 5.63 N/A 5.78 4.58 N/A 6.93 0.63
Sr 475 N/A 436 N/A 443 N/A 466 642 337 477 N/A 434 382 N/A 631 9
Y 12.58 N/A 11.99 N/A 12.30 N/A 12.56 12.08 11.77 13.52 N/A 13.71 11.24 N/A 17.19 1.11
Zr 51.88 N/A 48.59 N/A 54.42 N/A 50.32 54.97 47.73 58.74 N/A 53.78 48.40 N/A 71.87 4.25
Nb 1.98 N/A 1.82 N/A 2.19 N/A 2.26 2.49 1.78 2.40 N/A 1.97 2.07 N/A 3.42 0.45
Ba 147 N/A 133 N/A 147 N/A 160 264 110 153 N/A 138 123 N/A 223 4
La 4.96 N/A 4.65 N/A 5.52 N/A 4.95 7.93 4.00 5.83 N/A 5.03 4.57 N/A 7.55 0.37
Ce 12.07 N/A 11.48 N/A 13.39 N/A 13.84 17.65 10.58 14.32 N/A 13.61 11.64 N/A 17.82 0.85
Pr 1.68 N/A 1.51 N/A 1.84 N/A 1.72 2.28 1.45 1.96 N/A 1.72 1.52 N/A 2.40 0.35
Nd 7.94 N/A 8.05 N/A 8.56 N/A 8.16 10.76 7.22 9.69 N/A 8.15 7.43 N/A 11.35 0.51
Sm 2.21 N/A 2.58 N/A 2.26 N/A 2.01 2.27 1.85 2.63 N/A 2.11 1.94 N/A 2.67 0.37
Eu 0.85 N/A 0.76 N/A 0.89 N/A 0.89 1.00 0.73 0.93 N/A 0.82 0.74 N/A 1.16 0.41
Gd 2.51 N/A 1.96 N/A 2.40 N/A 2.23 2.45 2.06 2.73 N/A 3.13 1.86 N/A 3.07 0.37
Dy 2.18 N/A 2.40 N/A 2.43 N/A 2.50 2.75 2.22 2.84 N/A 2.44 2.00 N/A 3.38 0.42
Er 1.42 N/A 1.39 N/A 1.33 N/A 1.35 1.41 1.31 1.70 N/A 1.27 1.18 N/A 2.01 0.65
Yb 1.49 N/A 1.27 N/A 1.33 N/A 1.30 1.45 1.27 1.57 N/A 1.36 1.07 N/A 1.90 0.40
Hf 1.22 N/A 1.27 N/A 1.37 N/A 1.34 1.51 1.26 1.40 N/A 1.55 1.25 N/A 1.80 3.86
Ta 0.10 N/A 0.11 N/A 0.11 N/A 0.11 0.14 0.10 0.14 N/A 0.13 0.10 N/A 0.16 12.69
Pb 2.29 N/A 2.06 N/A 2.18 N/A 3.20 4.30 1.51 2.44 N/A 2.12 1.83 N/A 2.98 1.34
Th 0.60 N/A 0.58 N/A 0.55 N/A 0.60 1.28 0.49 0.62 N/A 0.62 0.54 N/A 1.01 1.01
U 0.24 N/A 0.26 N/A 0.51 N/A 0.31 0.55 0.16 0.30 N/A 0.27 0.23 N/A 0.37 0.04
133
BAS-44 B1 B2 B3 B6 B6-2 B7 B9 B17 B18 B20 B22 B23 B24 B25 BB2 BB3 BB4 s.d.
wt%
SiO2 48.89 47.78 48.23 49.50 48.91 49.04 48.51 48.61 49.08 49.01 48.68 49.12 48.78 49.64 48.59 49.15 49.04 0.35
TiO2 0.95 0.93 0.96 0.95 0.96 0.93 0.95 0.95 0.93 0.95 0.93 0.93 0.97 0.95 0.97 0.96 0.97 0.02
Al2O3 16.66 17.81 16.83 15.88 16.50 16.48 16.96 16.43 16.13 16.13 16.50 16.27 16.65 16.37 16.62 16.61 17.04 0.19
FeOT 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 8.88 0.08
MnO 0.13 0.13 0.11 0.13 0.11 0.13 0.11 0.12 0.12 0.12 0.13 0.12 0.11 0.13 0.11 0.12 0.12 0.01
MgO 9.52 9.64 10.13 9.78 9.72 9.86 9.55 10.04 10.21 9.63 10.02 9.82 9.59 10.43 9.76 9.33 9.38 0.07
CaO 10.48 10.48 10.57 10.38 10.53 10.55 10.66 10.44 10.08 10.57 10.45 10.41 10.61 10.66 10.64 10.72 10.34 0.11
Na2O 2.81 2.82 2.72 2.92 2.91 2.54 2.83 2.83 3.02 2.88 2.80 2.76 2.81 1.47 2.80 3.03 2.65 0.05
K2O 0.27 0.29 0.26 0.32 0.28 0.27 0.29 0.30 0.27 0.29 0.27 0.29 0.29 0.27 0.27 0.29 0.34 0.01
P2O5 0.17 0.14 0.16 0.16 0.15 0.16 0.15 0.15 0.16 0.16 0.15 0.16 0.16 0.16 0.15 0.16 0.15 0.01
S 0.11 0.10 0.11 0.11 0.11 0.12 0.12 0.11 0.12 0.12 0.11 0.12 0.12 0.10 0.12 0.11 0.10 0.00
Cl 0.026 0.031 0.029 0.025 0.024 0.026 0.029 0.025 0.029 0.025 0.030 0.025 0.027 0.031 0.033 0.025 0.028 0.00
CO2
(ppm) 494 413 554 446 575 505 654 557 835 615 489 357 784 336 649 90 334 37
H2O 1.14 1.02 1.04 1.01 0.93 1.08 0.99 1.16 1.02 1.26 1.11 1.14 1.07 0.95 1.12 0.64 1.00 0.04
PEC 5.85 7.57 8.19 6.81 6.87 6.91 6.72 6.84 6.21 7.09 6.82 7.43 6.98 7.83 7.05 4.81 6.56
Fo 87.4 87.7 88.2 87.7 87.7 87.7 87.5 88.1 88.3 87.6 88.0 87.7 87.5 87.7 87.8 87.3 87.1
ppm
Li 8.53 N/A 9.37 5.26 5.75 0.63 N/A 6.49 6.23 5.72 7.27 6.21 6.18 N/A 5.84 2.35 N/A 1.49
B 5.75 N/A 2.89 2.55 2.18 2.13 N/A 1.96 2.05 2.04 1.61 3.73 1.72 N/A 2.65 1.67 N/A 1.52
Sc 57.5 N/A 45.2 38.8 39.9 39.0 N/A 43.3 34.9 38.8 38.7 43.2 36.8 N/A 35.8 38.0 N/A 2.9
V 236 N/A 246 211 215 211 N/A 229 180 215 263 222 218 N/A 226 226 N/A 16
Rb 4.47 N/A 7.25 5.19 4.30 4.72 N/A 4.72 4.27 4.54 5.15 5.61 4.59 N/A 4.76 5.93 N/A 1.01
Sr 391 N/A 393 399 408 411 N/A 384 378 413 380 472 404 N/A 396 423 N/A 8
Y 19.59 N/A 19.44 17.88 18.48 19.53 N/A 18.99 17.97 17.72 c 19.35 18.11 N/A 17.99 18.00 N/A 3.00
Zr 79.0 N/A 83.5 77.3 76.6 84.3 N/A 77.6 74.3 72.5 78.9 79.7 74.4 N/A 77.6 79.2 N/A 6.2
Nb 2.57 N/A 2.98 2.67 2.93 2.84 N/A 2.65 2.36 2.59 2.62 3.27 2.63 N/A 2.48 2.79 N/A 1.02
Ba 112 N/A 125 118 111 115 N/A 107 98 108 97 177 109 N/A 104 129 N/A 4
La 7.43 N/A 7.43 7.50 7.57 7.15 N/A 6.96 7.20 7.52 7.26 7.89 7.17 N/A 7.56 7.85 N/A 0.79
Ce 20.6 N/A 22.1 18.6 19.8 18.7 N/A 19.4 17.5 19.4 19.2 21.0 19.2 N/A 20.2 20.5 N/A 1.4
Pr 2.63 N/A 2.83 2.59 2.62 2.72 N/A 2.69 2.58 2.71 2.58 2.83 2.72 N/A 2.61 2.66 N/A 0.83
Nd 12.0 N/A 12.3 11.5 13.0 12.5 N/A 11.9 12.1 12.0 12.2 13.7 11.6 N/A 12.4 12.7 N/A 1.0
Sm 3.0 N/A 2.4 3.0 3.1 3.1 N/A 2.7 2.6 2.9 2.6 3.1 2.8 N/A 3.0 2.9 N/A 1.0
Eu 0.86 N/A 1.09 1.07 1.05 0.97 N/A 1.07 0.94 0.99 1.05 1.12 1.05 N/A 1.18 0.90 N/A 0.85
Gd 3.14 N/A 3.23 3.09 3.22 3.29 N/A 3.18 3.14 3.25 3.20 3.22 2.86 N/A 3.17 3.38 N/A 0.88
Dy 3.34 N/A 3.66 3.36 3.45 3.61 N/A 3.80 3.04 3.11 3.33 3.15 3.31 N/A 3.25 0.00 N/A 1.72
Er 2.22 N/A 2.10 2.12 2.16 1.93 N/A 2.28 2.20 2.30 2.18 2.30 2.17 N/A 2.19 2.33 N/A 0.92
Yb 2.38 N/A 2.13 2.01 2.01 1.91 N/A 2.10 2.14 2.14 1.76 2.20 2.18 N/A 2.02 2.03 N/A 0.82
Hf 1.95 N/A 2.14 1.90 2.02 1.99 N/A 1.94 1.86 1.94 1.97 2.28 1.99 N/A 1.98 1.91 N/A 1.93
Ta 0.15 N/A 0.14 0.15 0.15 0.16 N/A 0.17 0.13 0.15 0.16 0.13 0.12 N/A 0.15 0.17 N/A 3.45
Pb 1.46 N/A 2.07 1.65 1.38 1.35 N/A 1.55 1.62 1.42 1.44 2.00 1.40 N/A 1.46 1.74 N/A 11.91
Th 0.54 N/A 0.61 0.60 0.67 0.59 N/A 0.57 0.58 0.53 0.58 0.62 0.56 N/A 0.60 0.66 N/A 1.71
U 0.20 N/A 0.26 0.21 0.22 0.19 N/A 0.23 0.19 0.18 0.25 0.25 0.19 N/A 0.20 0.29 N/A 0.02
134
B.2. Boron Isotope Compositions
Sample δ11B 2SE Sample δ11B 2SE
LCC-9-S-
06 -12.63 1.30 BRVB-S-11 -4.69 1.20
LCC-9-S-
07 -11.67 1.24 BRVB-S-14 -5.20 1.08
LCC-9-S-
01 -11.49 1.48 BRVB-S-01 -4.62 1.28
LCC-9-S-
09 -8.79 1.03 BRVB-S-09 -5.38 1.37
LCC-2-S-
07 -5.30 1.86 BPB-S-02 -5.84 1.61
LCC-2-S-
03 -7.98 1.36 BPB-S-04 -3.90 1.62
LCC-2-S-
06 -13.09 1.51 BPB-S-07 -5.53 1.48
LCC-2-S-
10 -8.18 1.32 BRM-S-08 -3.60 1.92
BORG-S-
01 -3.50 2.24 BRM-S-09 -3.17 1.61
BORG-S-
04 -4.21 1.75 BRM-S-03 -2.10 1.54
BORG-S-
10 -3.42 1.81 BRM-S-05 -0.65 1.75
BORG-S-9 1.52 1.68 BPPC-S-04 -4.90 1.60
BORG-S-6 -0.82 1.98 BPPC-S-07 -5.40 1.60
BORG-S-
13 -5.43 1.68 BPPC-S-11 -5.28 1.71
BBL-S-11 -2.89 2.35 BPPC-S-01 -4.23 2.67
BBL-S-06 -7.21 4.16 BAS-44-S-
08 -3.22 4.36
BBL-S-08 -2.78 2.57 BAS-44-S-
06 -6.75 1.55
BBL-S-04 -5.10 3.21 BAS-44-S-
01 -2.78 2.71
BBL-S-05 -3.24 1.10 BAS-44-S-
01 -5.38 2.90
135
B.3. Radiogenic Isotope Compositions
Sample ID BPCB-1 BORG-1 BPB-1 BBL-05 BAS-44-01 BRVB-1
208Pb/204Pb 38.4640093 38.5386438 38.612363 38.6502638 38.56384767 38.6456054
2SE 0.0027 0.00226 0.00382 0.00206 0.00242 0.00218
207Pb/204Pb 15.5897941 15.6012692 15.612799 15.6183439 15.60589745 15.6166351
2SE 0.001028 0.001022 0.001204 0.000878 0.000878 0.000832
206Pb/204Pb 18.8429231 18.8979534 18.954407 18.9642892 18.92165526 18.977124
2SE 0.00118 0.001138 0.00103 0.001004 0.00091 0.000884
143Nd/144Nd 0.512926 0.51286409 0.5128272 0.51285886 0.512948154 0.51283266
2SE 0.00000594 0.00000642 6.46E-06 0.00000582 0.0000056 0.00000644
176Hf/177Hf 0.28305201 0.28305515 0.2830588 0.28305717 0.283093557 0.28303467
2SE 0.00000722 0.00000646 8.86E-06 0.00000626 0.00000622 0.00000532
87Sr/86Sr 0.70339631 0.70381332 0.7038772 0.70393874 0.703528686 0.70398503
2SE 0.000006 0.000008 0.000008 0.000007 0.000008 0.000008
136
APPENDIX C
CHAPTER IV SUPPLEMENTARY MATERIALS
C.1. PEC Corrected Melt Inclusion Compositions
Data in this table represent individual melt inclusion compositions that have been
corrected for Fe loss and post entrapment crystallization (PEC). Major elements were
restored using Petrolog 3.1.1 (Danyushevsky and Plechov, 2011). H2O, Cl, S, and trace
elements were restored by the same percent as K2O because they are incompatible with
olivine. H2O values in this table are not corrected for H+ diffusive loss (i.e. they are
different from values shown Fig. 4.6). CO2 values were corrected using methods
described in the text modified from Wallace et al. (2015) and Aster et al. (in prep).
Analyzed CO2 concentrations for these inclusions are reported in C.2. FeO and Fe2O3
were calculated using Petrolog 3.1.1 assuming an fO2 of QFM +1. Temperatures are
calculated by Petrolog 3.1.1 and represent temperatures of melt inclusion entrapment.
Major element standard deviations represent an average of those calculated for each melt
inclusion based on three EPMA point analyses. Trace element standard deviations are
also an average from individual inclusions based on the methods of Loewen and Kent
(2012).
137
LCC 9-01 9-02 9-06 9-07
09-
09 9-04
9-
04(2) 9-10
9-
16(1)
9-
16(2)
9-
18(1) S.D.
wt%
SiO2 50.64 49.76 49.47 50.23 50.28 50.17 50.41 50.29 49.53 49.43 50.40 0.34
TiO2 0.84 0.91 0.83 0.80 0.77 0.82 0.80 0.78 0.80 0.81 0.80 0.03
Al2O3 16.06 17.37 15.94 16.03 15.88 16.23 16.00 16.21 15.88 15.93 15.85 0.27
Fe2O3 1.05 1.01 1.02 1.01 1.02 1.03 1.03 1.03 1.03 1.02 1.04
FeO 6.06 6.10 6.09 6.10 6.09 6.08 6.08 6.08 6.08 6.09 6.07 0.13
MnO 0.09 0.09 0.08 0.09 0.08 0.08 0.08 0.08 0.10 0.09 0.09 0.01
MgO 8.93 8.42 9.47 9.41 9.51 8.86 8.94 9.29 9.26 9.28 9.20 0.75
CaO 9.74 9.10 10.27 9.76 9.37 9.85 9.55 9.75 10.30 10.34 9.81 0.22
Na2O 3.13 3.32 2.78 2.67 2.74 3.06 2.92 2.92 2.87 2.82 2.96 0.16
K2O 0.83 0.81 0.69 0.79 0.79 0.78 0.85 0.79 0.66 0.66 0.76 0.03
P2O5 0.16 0.17 0.16 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.15 0.01
S 0.08 0.09 0.09 0.09 0.05 0.09 0.08 0.09 0.09 0.09 0.09 0.003
Cl 0.034 0.037 0.037 0.034 0.037 0.037 0.034 0.036 0.035 0.036 0.035 0.003
H2O 2.59 3.06 3.35 3.11 3.47 3.02 3.32 2.75 3.51 3.53 3.01 0.25
CO2 (ppm)
RESTORED 2180 1011 3298 1252 2101 1371 1727 2912 3030 3101 2792 91
T C 1254 1247 1260 1260 1267 1251 1254 1260 1255 1255 1258
Fo 89.7 89.2 90.2 90.0 90.1 89.6 89.6 90.0 90.0 90.0 89.9
% PEC 9.7 5.0 11.8 4.4 11.5 9.6 10.4 11.2 9.7 10.0 10.2
ppm
Li
5.84 9.69 15.76 7.24 7.60
4.84 7.55
1.93
B
7.20 5.43 6.54 2.30 5.04
3.83 5.32
2.83
Sc
29.83 30.58 31.34 27.11 26.57
29.25 28.73
1.58
V
196 206 178 175 190
192 209
12
Rb
10.20 17.03 14.00 13.74 13.32
9.42 11.75
0.69
Sr
347 371 368 349 339
321 331
9
Y
15.37 14.13 15.67 13.28 12.86
13.25 12.37
0.81
Zr
80.96 75.83 89.94 72.31 67.69
67.79 63.42
4.59
Nb
4.46 4.34 4.06 4.07 3.90
4.17 4.10
0.35
Ba
178 206 207 200 186
157 160
6
La
8.38 7.83 8.08 7.59 7.03
6.57 6.44
0.28
Ce
17.96 17.62 18.47 16.93 16.53
15.46 16.09
0.68
Pr
2.50 2.32 2.74 2.55 2.25
2.18 1.99
0.14
Nd
10.96 10.36 15.07 11.42 10.49
9.21 9.66
0.57
Sm
2.22 2.61 2.07 2.48 2.27
2.26 2.05
0.24
Eu
1.03 0.90 1.09 0.80 0.80
0.79 0.81
0.08
Gd
3.04 2.74 2.87 2.77 2.51
2.30 2.65
0.17
Dy
2.63 2.56 2.66 3.05 2.27
2.45 2.27
0.17
Er
1.66 1.38 2.46 1.22 1.39
1.61 1.52
0.12
Yb
1.43 1.60 1.74 1.56 1.27
1.30 1.48
0.12
Hf
1.77 1.92 3.46 1.92 1.56
1.70 1.15
0.18
Ta
0.28 0.25 0.43 0.18 0.24
0.27 0.26
0.05
Pb
2.40 2.91 2.87 2.90 2.80
1.66 2.13
0.20
Th
1.29 1.65 1.66 1.66 1.53
1.12 0.99
0.12
U 0.35 0.51 0.54 0.58 0.46 0.37 0.37 0.05
138
LCC-7-
02
LCC-7-
03
LCC-7-
04
LCC-7-
05
LCC-7-
08
LCC-7-
10 S.D.
wt%
SiO2 50.23 50.78 50.48 50.75 50.24 50.27 0.23
TiO2 0.76 0.76 0.78 0.77 0.77 0.78 0.02
Al2O3 16.05 15.86 15.84 15.49 15.86 15.68 0.13
Fe2O3 0.99 1.04 1.04 1.02 1.02 1.03
FeO 6.11 6.07 6.07 6.08 6.08 6.08 0.06
MnO 0.07 0.08 0.08 0.09 0.08 0.08 0.01
MgO 9.73 9.50 9.77 9.70 9.03 9.25 0.12
CaO 10.47 10.22 10.63 9.41 10.06 10.18 0.07
Na2O 2.59 2.95 2.89 2.60 2.92 2.84 0.12
K2O 0.60 0.65 0.61 0.77 0.69 0.66 0.02
P2O5 0.12 0.14 0.13 0.12 0.14 0.14 0.01
S 0.09 0.09 0.08 0.08 0.08 0.07 0.001
Cl 0.038 0.039 0.039 0.037 0.039 0.039 0.001
H2O 2.36 2.04 1.76 3.34 3.24 3.16 0.16
CO2 (ppm)
RESTORED 2801 2356 N/A 1592 2009 2465 75
T C 1260 1261 1264 1269 1252 1255
Fo 90.3 90.2 90.5 90.2 89.7 89.9
% PEC 13.2 10.3 12.0 10.1 9.5 10.5
ppm
Li
17.02 7.11 7.32 1.72
B
4.42 6.37 3.52 2.14
Sc
28.86 29.44 26.14 1.57
V
190 206 220 13
Rb
14.06 13.40 13.18 0.65
Sr
321 338 333 6
Y
13.54 13.84 12.20 0.85
Zr
70.47 72.06 65.83 4.23
Nb
4.02 4.25 4.33 0.34
Ba
195 185 177 5
La
7.39 7.07 6.34 0.23
Ce
15.97 16.51 15.54 0.47
Pr
2.10 2.19 2.04 0.08
Nd
9.08 9.22 9.12 0.39
Sm
2.30 2.49 2.02 0.13
Eu
0.82 0.85 0.75 0.06
Gd
2.53 2.30 2.15 0.22
Dy
2.32 2.63 2.30 0.09
Er
1.35 1.48 1.20 0.09
Yb
1.57 1.38 1.21 0.07
Hf
1.69 1.67 1.65 0.13
Ta
0.19 0.25 0.27 0.03
Pb
3.95 2.82 2.42 0.19
Th
1.27 1.18 1.01 0.09
U 0.43 0.43 0.38 0.03
139
LCC-6-
01
LCC-6-
02
LCC-6-
06
LCC-6-
07
LCC-6-
08
LCC-6-
10 S.D.
wt%
SiO2 49.92 51.00 50.05 50.57 50.29 53.65 0.31
TiO2 0.82 0.81 0.85 0.84 0.82 0.70 0.02
Al2O3 16.14 16.08 16.38 16.02 16.94 15.67 0.11
Fe2O3 1.03 1.02 1.00 1.02 0.99 1.12
FeO 6.08 6.09 6.10 6.09 6.11 6.00 0.04
MnO 0.07 0.08 0.11 0.10 0.08 0.09 0.01
MgO 9.57 8.83 9.16 8.87 9.02 9.02 0.07
CaO 9.87 9.48 9.70 9.61 9.89 7.24 0.07
Na2O 2.90 2.95 2.82 2.94 2.91 3.15 0.25
K2O 0.70 0.78 0.75 0.78 0.77 1.45 0.02
P2O5 0.15 0.15 0.16 0.16 0.15 0.15 0.01
S 0.09 0.09 0.08 0.09 0.09 0.06 0.003
Cl 0.040 0.037 0.038 0.038 0.039 0.032 0.002
H2O 2.87 2.85 3.04 3.13 2.11 1.84 0.16
CO2 (ppm)
RESTORED 2924 1782 2300 3025 1534 0 77
T C 1266 1251 1255 1251 1250 1284
Fo 90.3 89.4 89.8 89.5 89.7 89.7
% PEC 12.1 11.5 10.1 10.1 10.9 13.1
ppm
Li 9.04 7.04 9.05
35.27 2.62
B 3.56 3.30 5.27
13.09 3.03
Sc 24.70 24.93 26.13
20.54 1.28
V 242 189 196
134 14
Rb 14.32 15.52 15.01
27.66 0.83
Sr 344 351 344
316 8
Y 13.42 13.08 13.44
13.12 0.84
Zr 67.77 68.02 70.46
68.45 4.49
Nb 5.03 4.37 4.63
4.69 0.41
Ba 177 195 189
312 5
La 7.05 7.86 7.32
9.51 0.29
Ce 17.91 18.16 16.88
19.91 0.54
Pr 2.11 2.08 2.07
2.47 0.10
Nd 10.04 9.53 10.09
11.15 0.33
Sm 2.38 2.39 2.34
2.44 0.20
Eu 0.81 0.79 0.81
1.06 0.08
Gd 3.02 2.65 2.68
2.44 0.19
Dy 2.30 2.38 2.15
2.53 0.13
Er 1.64 1.19 1.38
1.36 0.12
Yb 1.48 1.46 1.32
1.73 0.14
Hf 1.80 1.84 1.84
1.72 0.14
Ta 0.28 0.27 0.26
0.34 0.04
Pb 2.88 3.02 2.80
8.29 0.28
Th 1.08 1.58 1.44
3.26 0.14
U 0.38 0.42 0.48 1.62 0.06
140
LCC
5-
01(MI_1)
5-
01(MI_2) 5-03 5-04 5-05 5-07
5-
11(MI_1)
5-
11(MI_3) 5-12 S.D.
wt%
SiO2 50.83 50.94 52.20 54.25 51.45 51.84 53.89 55.30 51.46 0.22
TiO2 0.81 0.81 0.87 0.77 0.89 0.85 0.67 0.67 0.78 0.02
Al2O3 16.13 15.76 15.90 15.86 15.87 16.29 15.11 15.28 16.57 0.14
Fe2O3 1.05 1.06 1.10 1.13 1.10 1.04 1.23 1.02 1.06
FeO 6.06 6.04 6.01 5.99 6.02 6.06 5.90 6.09 6.05 0.08
MnO 0.09 0.09 0.08 0.10 0.07 0.08 0.10 0.11 0.10 0.02
MgO 8.56 8.56 8.38 8.37 8.61 8.60 8.30 9.28 7.87 0.18
CaO 9.81 9.72 9.60 7.52 9.73 10.04 6.92 6.97 9.56 0.14
Na2O 3.20 3.25 3.55 3.43 3.54 3.21 3.69 1.94 3.41 0.19
K2O 0.85 0.82 0.91 1.46 0.82 0.85 1.77 1.72 1.03 0.02
P2O5 0.16 0.16 0.16 0.16 0.17 0.16 0.13 0.13 0.17 0.01
S 0.09 0.09 0.06 0.08 0.10 0.08 0.06 0.06 0.08 0.003
Cl 0.037 0.036 0.039 0.035 0.036 0.040 0.035 0.035 0.037 0.001
H2O 2.53 2.90 1.28 1.00 1.79 1.03 2.39 1.56 2.01 0.28
CO2 (ppm)
RESTORED 2555 2677 1751 1052 908 2705 0 0 2055 106
T C 1245 1247 1246 1269 1251 1242 1284 1277 1231
Fo 89.3 89.3 89.2 89.1 89.5 89.3 89.3 89.3 88.5
% PEC 8.8 9.6 6.8 12.1 11.4 9.9 11.7 13.8 8.3
ppm
Li
9.17 33.23
51.64
11.13 4.95
B
5.36 10.20
12.39
5.33 4.29
Sc
26.06 18.91
18.28
21.07 1.23
V
186 142
139
180 11
Rb
15.63 28.26
33.25
22.00 1.03
Sr
350 328
296
376 8
Y
13.71 14.07
12.81
12.51 0.83
Zr
76.08 76.37
67.65
70.25 4.45
Nb
4.75 5.21
4.64
4.67 0.42
Ba
208 332
323
243 7
La
8.41 10.56
9.30
8.75 0.27
Ce
18.32 21.67
20.47
19.14 0.56
Pr
2.35 2.52
2.33
2.49 0.09
Nd
9.91 11.45
10.19
10.35 0.40
Sm
2.19 2.41
2.19
2.74 0.20
Eu
0.76 0.77
0.65
0.78 0.06
Gd
2.26 2.55
2.63
2.26 0.17
Dy
2.17 2.49
2.02
2.31 0.13
Er
1.49 1.47
1.39
1.41 0.07
Yb
1.27 1.46
1.74
1.30 0.07
Hf
1.90 1.52
1.72
1.79 0.13
Ta
0.28 0.38
0.31
0.24 0.05
Pb
3.14 9.74
9.82
3.81 0.47
Th
1.60 2.69
2.84
1.46 0.17
U 0.54 1.51 1.63 0.45 0.10
141
LCC-4-
05
LCC-4-
06(MI_1) LCC-4-13 avg 1 s.d.
wt%
SiO2 52.66 52.08 50.73 0.42
TiO2 0.93 0.94 0.92 0.02
Al2O3 16.64 17.25 16.28 0.07
Fe2O3 1.10 1.03 1.07
FeO 6.02 6.10 6.05 0.04
MnO 0.10 0.08 0.07 0.01
MgO 8.56 7.57 8.65 0.06
CaO 8.33 9.60 9.54 0.09
Na2O 3.25 3.45 3.38 0.06
K2O 1.56 1.00 0.84 0.01
P2O5 0.19 0.18 0.18 0.003
S 0.02 0.06 0.10 0.004
Cl 0.042 0.039 0.046 0.002
H2O 0.71 0.73 2.39 0.28
CO2 (ppm)
RESTORED 1711 3702 2655 99
T C 1262 1219 1252
Fo 89.4 88.0 89.5
% PEC 15.6 9.5 10.5
ppm
Li 6.24 68.95
5.96
B 3.35 23.12
4.57
Sc 20.48 27.77
1.45
V 148 194
13
Rb 11.19 53.70
1.08
Sr 278 461
8
Y 9.84 19.25
1.25
Zr 54.70 105.92
6.77
Nb 3.95 7.92
0.49
Ba 160 515
10
La 6.47 14.92
0.31
Ce 15.21 33.70
0.69
Pr 1.85 3.65
0.13
Nd 7.87 15.52
0.46
Sm 1.87 3.05
0.32
Eu 0.65 1.03
0.08
Gd 1.85 3.98
0.27
Dy 1.92 3.82
0.26
Er 1.10 2.23
0.12
Yb 1.13 2.13
0.14
Hf 1.26 3.29
0.21
Ta 0.28 0.57
0.05
Pb 2.62 14.00
0.57
Th 1.24 4.78
0.17
U 0.32 2.89 0.09
142
LCC-2-
01
LCC-2-
02
LCC-2-
04
LCC-2-
05
LCC-2-
07
LCC-2-
08
LCC-2-
09
LCC-2-
10 S.D.
wt%
SiO2 50.98 50.96 50.60 50.55 50.57 50.76 50.83 49.99 0.26
TiO2 0.96 0.94 0.95 0.97 0.95 0.94 0.94 0.92 0.02
Al2O3 16.54 16.66 16.57 17.04 16.85 17.03 16.87 16.74 0.11
Fe2O3 1.07 1.00 1.03 1.04 1.06 1.03 1.05 1.05
FeO 6.04 6.10 6.08 6.06 6.05 6.08 6.06 6.06 0.07
MnO 0.09 0.08 0.08 0.09 0.08 0.09 0.09 0.09 0.01
MgO 7.94 8.32 8.24 8.20 8.18 7.66 7.98 8.12 0.05
CaO 9.53 9.07 9.24 9.39 9.47 9.50 9.47 9.41 0.05
Na2O 3.58 2.91 3.22 3.42 3.49 3.43 3.46 3.40 0.14
K2O 0.89 0.95 0.90 0.92 0.91 0.91 0.91 0.89 0.01
P2O5 0.19 0.20 0.20 0.20 0.20 0.20 0.20 0.19 0.01
S 0.09 0.09 0.09 0.09 0.09 0.10 0.09 0.09 0.003
Cl 0.037 0.037 0.038 0.038 0.039 0.039 0.038 0.039 0.002
H2O 2.27 2.93 2.99 2.19 2.27 2.46 2.22 3.25 0.18
CO2 (ppm)
RESTORED 1541 1902 2904 2096 2021 1852 1522 2288 62
T C 1235 1240 1241 1240 1240 1224 1234 1240
Fo 88.7 88.8 88.9 89.0 89.0 88.2 88.7 88.9
% PEC 7.9 9.0 9.2 8.1 8.1 6.2 7.5 8.4
ppm
Li 10.53
7.71
9.59 8.50
1.43
B 6.57
4.77
6.69 6.08
2.70
Sc 26.02
24.16
27.18 27.57
1.37
V 256
191
195 200
13
Rb 24.05
16.82
17.06 17.67
0.78
Sr 392
379
377 388
8
Y 13.90
14.32
14.96 15.32
0.86
Zr 81.28
85.86
86.72 86.62
5.04
Nb 6.69
6.07
6.69 6.31
0.51
Ba 234
228
232 233
6
La 9.13
8.99
9.36 9.53
0.25
Ce 22.40
20.42
21.42 21.04
0.51
Pr 2.66
2.60
2.64 2.69
0.10
Nd 12.04
11.70
12.07 12.03
0.38
Sm 2.54
2.17
2.75 2.86
0.21
Eu 0.84
0.89
0.88 0.90
0.06
Gd 2.66
2.65
2.84 2.61
0.15
Dy 2.77
2.68
2.72 2.59
0.13
Er 1.46
1.73
1.52 1.65
0.13
Yb 1.04
1.70
1.52 1.14
0.16
Hf 1.94
1.72
1.84 2.14
0.15
Ta 0.34
0.33
0.35 0.35
0.04
Pb 3.91
2.95
2.97 3.48
0.19
Th 1.70
1.43
1.61 1.72
0.11
U 0.61 0.48 0.48 0.50 0.04
143
C.2. Analyzed (uncorrected) Melt Inclusion Compositions
LCC 9-01 9-02 9-06 9-07
9-
09(1)
9-
09(2) 9-04
9-
04(2) 9-10 9-13
9-
16(1)
9-
16(2)
9-
18(1)
1
S.D.
wt%
SiO2 51.04 49.89 50.48 50.57 51.04 51.44 50.89 51.28 51.15 53.14 49.96 50.10 51.18 0.34
Al2O
3 17.42 18.12 17.82 16.72 17.20 17.73 17.72 17.61 17.95 17.70 17.27 17.45 17.39 0.27
FeOT 5.34 5.39 4.99 5.18 4.94 5.05 5.30 5.25 5.18 6.21 5.46 5.31 5.21 0.13
MgO 5.71 7.15 5.72 8.59 5.80 5.88 5.77 5.58 5.67 4.87 6.03 6.05 5.94 0.75
CaO 10.57 9.49 11.48 10.17 10.73 10.46 10.76 10.51 10.79 8.92 11.20 11.32 10.77 0.22
Na2
O 3.39 3.46 3.11 2.78 3.19 3.06 3.34 3.22 3.23 3.72 3.12 3.09 3.24 0.16
K2O 0.90 0.85 0.77 0.82 0.83 0.88 0.85 0.93 0.87 1.35 0.71 0.72 0.83 0.03
TiO2 0.91 0.95 0.93 0.83 0.85 0.86 0.89 0.88 0.86 0.85 0.87 0.89 0.87 0.03
Mn
O 0.10 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.11 0.10 0.10 0.10 0.01
P2O5 0.17 0.18 0.18 0.16 0.16 0.16 0.17 0.16 0.17 0.16 0.17 0.16 0.16 0.01
S 0.09 0.09 0.10 0.09 0.09 0.06 0.10 0.09 0.10 0.08 0.10 0.10 0.09 0.003
Cl 0.04 0.04 0.04 0.03 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.003
CO2
(ppm) 965 947 1402 1252 0 848 560 679 1227 648 1500 1545 1339 91
H2O 2.70 3.07 3.59 3.11 3.00 3.71 3.16 3.51 2.92 2.43 3.66 3.71 3.17 0.25
ppm
Li
6.28 9.78 17.32 7.87 8.35
26.82 5.26 8.21
1.93
B
7.74 5.49 7.19 2.50 5.54
10.25 4.17 5.78
2.83
Sc
32.07 30.89 34.44 29.46 29.19
25.71 31.79 31.23
1.58
V
211 209 195 190 209
177 209 227
11.89
Ni
68.29
274.7
5
175.4
0 62.74
232.5
1
47.50 84.43 57.81
20.22
Rb
10.97 17.20 15.39 14.93 14.64
28.57 10.23 12.78
0.69
Sr
373 375 405 379 373
380 349 360
8.53
Y
16.53 14.27 17.22 14.43 14.13
13.86 14.40 13.45
0.81
Zr
87.06 76.60 98.84 78.59 74.38
79.53 73.69 68.94
4.59
Nb
4.80 4.39 4.46 4.42 4.29
4.25 4.53 4.46
0.35
Ba
191 208 227 217 205
305 171 174
5.96
La
9.01 7.90 8.87 8.25 7.73
9.55 7.14 7.00
0.28
Ce
19.32 17.80 20.30 18.40 18.16
20.52 16.80 17.49
0.68
Pr
2.68 2.34 3.02 2.77 2.48
2.53 2.36 2.17
0.14
Nd
11.78 10.46 16.56 12.41 11.53
12.56 10.01 10.50
0.57
Sm
2.38 2.64 2.27 2.70 2.49
2.52 2.46 2.23
0.24
Eu
1.11 0.91 1.19 0.87 0.88
0.86 0.86 0.88
0.08
Gd
3.27 2.77 3.16 3.01 2.76
2.53 2.51 2.88
0.17
Dy
2.82 2.59 2.92 3.32 2.50
2.56 2.66 2.47
0.17
Er
1.79 1.39 2.71 1.33 1.52
1.55 1.75 1.65
0.12
Yb
1.53 1.61 1.92 1.69 1.39
1.43 1.42 1.61
0.12
Hf
1.91 1.94 3.80 2.09 1.71
1.98 1.85 1.26
0.18
Ta
0.30 0.25 0.48 0.20 0.26
0.26 0.29 0.29
0.05
Pb
2.58 2.94 3.15 3.15 3.08
7.18 1.80 2.31
0.20
Th
1.39 1.66 1.82 1.80 1.68
2.48 1.22 1.08
0.12
U 0.38 0.51 0.59 0.63 0.50 0.83 0.40 0.40 0.05
144
LCC-7-
02
LCC-7-
03
LCC-7-
04
LCC-7-
05
LCC-7-
08
LCC-7-
10
1
S.D.
wt%
SiO2 51.17 51.51 51.47 52.01 51.34 51.48 0.23
Al2O3 18.05 17.38 17.68 17.13 17.43 17.39 0.13
FeOT 4.77 4.96 4.80 5.80 4.89 4.82 0.06
MgO 5.54 6.37 6.07 6.28 6.30 6.18 0.12
CaO 11.78 11.21 11.86 10.40 11.06 11.29 0.07
Na2O 2.91 3.23 3.23 2.87 3.21 3.15 0.12
K2O 0.68 0.72 0.68 0.85 0.76 0.73 0.02
TiO2 0.86 0.83 0.87 0.86 0.85 0.86 0.02
MnO 0.08 0.09 0.08 0.10 0.08 0.09 0.01
P2O5 0.14 0.15 0.15 0.14 0.15 0.16 0.01
S 0.10 0.10 0.08 0.09 0.09 0.07 0.001
Cl 0.04 0.04 0.04 0.04 0.04 0.04 0.001
CO2
(ppm) 974 1159 1014 654 1043 1198 75
H2O 2.54 2.14 1.88 3.54 3.42 3.36 0.16
ppm
Li
18.50 7.64 7.96 1.72
B
4.81 6.85 3.82 2.14
Sc
31.37 31.66 28.41 1.57
V
207 221 239 13
Ni
78.33 107.05 105.84 10.79
Rb
15.28 14.41 14.33 0.65
Sr
349 363 362 6
Y
14.72 14.88 13.26 0.85
Zr
76.60 77.49 71.55 4.23
Nb
4.37 4.57 4.70 0.34
Ba
212 199 192 5
La
8.03 7.60 6.89 0.23
Ce
17.36 17.76 16.89 0.47
Pr
2.29 2.36 2.21 0.08
Nd
9.87 9.91 9.91 0.39
Sm
2.50 2.67 2.20 0.13
Eu
0.89 0.91 0.81 0.06
Gd
2.75 2.47 2.33 0.22
Dy
2.53 2.83 2.50 0.09
Er
1.47 1.59 1.30 0.09
Yb
1.71 1.48 1.31 0.07
Hf
1.83 1.80 1.79 0.13
Ta
0.20 0.27 0.29 0.03
Pb
4.29 3.03 2.63 0.19
Th
1.39 1.27 1.10 0.09
U 0.47 0.46 0.41 0.03
145
LCC-6-01
LCC-6-
02
LCC-6-
06
LCC-6-
07
LCC-6-
08
LCC-6-
10
1
S.D.
wt%
SiO2 50.72 52.26 50.43 51.18 49.98 55.27 0.31
Al2O3 17.98 17.96 17.84 17.51 18.30 17.70 0.11
FeO 4.96 4.81 5.47 5.23 4.69 5.62 0.04
MgO 5.70 5.27 5.73 5.58 5.56 4.31 0.07
CaO 11.00 10.58 10.56 10.50 10.68 8.17 0.07
Na2O 3.23 3.29 3.07 3.21 3.14 3.56 0.25
K2O 0.78 0.88 0.82 0.86 0.83 1.63 0.02
TiO2 0.91 0.90 0.92 0.91 0.89 0.80 0.02
MnO 0.08 0.08 0.12 0.11 0.08 0.11 0.01
P2O5 0.16 0.17 0.17 0.17 0.16 0.17 0.01
S 0.10 0.10 0.09 0.09 0.10 0.07 0.003
Cl 0.04 0.04 0.04 0.04 0.04 0.04 0.002
CO2
(ppm) 1147 633 970 1426 583 1290 77
H2O 3.06 3.06 3.18 3.29 2.19 1.99 0.16
ppm
Li 10.04 7.73 9.94
40.54 2.62
B 3.95 3.63 5.79
15.05 3.03
Sc 27.45 27.40 28.72
23.61 1.28
V 269 208 215
154 14
Ni 389.75 72.98 148.33
18.70 32.28
Rb 15.91 17.05 16.49
31.80 0.83
Sr 382 385 378
364 8
Y 14.91 14.37 14.77
15.09 0.84
Zr 75.30 74.75 77.43
78.67 4.49
Nb 5.59 4.80 5.08
5.40 0.41
Ba 197 214 207
359 5
La 7.84 8.64 8.05
10.93 0.29
Ce 19.91 19.95 18.55
22.89 0.54
Pr 2.35 2.29 2.28
2.84 0.10
Nd 11.15 10.47 11.08
12.82 0.33
Sm 2.64 2.63 2.57
2.80 0.20
Eu 0.90 0.87 0.89
1.22 0.08
Gd 3.36 2.92 2.95
2.80 0.19
Dy 2.55 2.61 2.36
2.91 0.13
Er 1.82 1.30 1.51
1.57 0.12
Yb 1.64 1.60 1.45
1.98 0.14
Hf 2.00 2.03 2.02
1.98 0.14
Ta 0.31 0.29 0.29
0.39 0.04
Pb 3.19 3.32 3.08
9.53 0.28
Th 1.20 1.74 1.58
3.75 0.14
U 0.42 0.47 0.53 1.86 0.06
146
5-
01(MI_1)
5-
01(MI_2) 5-03 5-04 5-05 5-07
5-
11(MI_1)
5-
11(MI_3) 5-12 5-13
1
S.D.
wt%
reentrant
SiO2 50.35 50.64 52.53 56.06 52.25 51.00 54.70 55.71 51.28 55.66 0.22
Al2O3 17.08 16.84 16.83 17.83 17.54 17.24 16.66 16.90 17.57 17.23 0.14
FeOT 5.41 5.03 4.79 5.95 4.53 5.01 5.78 6.00 5.93 5.81 0.08
MgO 5.55 5.43 6.68 3.87 5.15 5.27 3.92 3.94 4.78 3.69 0.18
CaO 10.39 10.39 10.16 8.46 10.75 10.63 7.63 7.71 10.13 7.91 0.14
Na2O 3.39 3.47 3.76 3.86 3.91 3.40 4.07 2.15 3.62 4.02 0.19
K2O 0.90 0.88 0.97 1.64 0.91 0.90 1.95 1.90 1.09 1.87 0.02
TiO2 0.86 0.86 0.92 0.86 0.98 0.90 0.74 0.74 0.83 0.74 0.02
MnO 0.10 0.10 0.09 0.11 0.08 0.08 0.11 0.12 0.11 0.11 0.02
P2O5 0.17 0.17 0.17 0.18 0.19 0.17 0.14 0.14 0.18 0.16 0.01
S 0.09 0.09 0.06 0.08 0.10 0.08 0.06 0.06 0.08 0.06 0.003
Cl 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.001
CO2
(ppm) 1259 1283 786 198 1093 1300 1484 317 813 141 106
H2O 2.58 2.98 1.31 1.08 1.90 1.04 2.53 1.65 2.05 1.13 0.28
ppm
Li
10.54 37.77
60.05
12.10 43.23 4.95
B
6.16 11.59
14.41
5.79 14.93 4.29
Sc
29.96 21.49
21.26
22.90 18.54 1.23
V
214 161
161
196 151 11
Ni
280.29 27.14
663.83
215.13 29.76 74.65
Rb
17.96 32.12
38.67
23.92 40.48 1.03
Sr
403 373
344
409 346 8
Y
15.76 15.99
14.90
13.60 14.72 0.83
Zr
87.45 86.78
78.67
76.36 81.45 4.45
Nb
5.46 5.92
5.39
5.08 5.80 0.42
Ba
239 377
375
264 386 7
La
9.67 12.00
10.81
9.51 11.15 0.27
Ce
21.06 24.62
23.80
20.81 23.18 0.56
Pr
2.70 2.87
2.71
2.70 2.83 0.09
Nd
11.39 13.01
11.85
11.25 12.18 0.40
Sm
2.52 2.74
2.55
2.98 2.43 0.20
Eu
0.87 0.88
0.76
0.85 0.80 0.06
Gd
2.60 2.90
3.05
2.46 2.72 0.17
Dy
2.50 2.83
2.35
2.51 2.69 0.13
Er
1.71 1.68
1.61
1.53 1.60 0.07
Yb
1.46 1.66
2.02
1.41 1.73 0.07
Hf
2.18 1.73
2.01
1.95 1.98 0.13
Ta
0.33 0.43
0.36
0.26 0.48 0.05
Pb
3.61 11.07
11.42
4.14 11.59 0.47
Th
1.84 3.05
3.30
1.59 3.71 0.17
U 0.62 1.72 1.89 0.49 2.19 0.10
147
LCC-4-
01
LCC-4-
05 LCC-4-06(MI_1) LCC-4-06(MI_2)
LCC-4-
08 1 S.D.
wt% reentrant
reentrant
SiO2 52.29 54.49 51.08 55.38 56.67 0.42
Al2O3 18.46 19.23 18.14 17.38 18.22 0.07
FeOT 4.34 5.63 4.79 5.80 5.93 0.04
MgO 3.39 2.75 4.48 3.68 2.86 0.06
CaO 10.67 9.62 10.10 7.77 7.87 0.09
Na2O 4.01 3.76 3.63 4.21 4.15 0.06
K2O 0.91 1.80 1.05 1.94 1.97 0.01
TiO2 1.00 1.07 0.99 0.77 0.81 0.02
MnO 0.08 0.11 0.09 0.11 0.12 0.01
P2O5 0.21 0.22 0.19 0.18 0.18 0.003
S 0.10 0.02 0.06 0.04 0.10 0.004
Cl 0.05 0.05 0.04 0.04 0.04 0.002
CO2
(ppm) 671 251 -105 1323 1046 99
H2O 1.94 0.79 0.74 2.20 2.31 0.28
ppm
Li 63.09 7.52 74.95 11.31
5.96
B 10.38 4.04 25.13 5.43
4.57
Sc 34.09 24.68 30.18 27.77
1.45
V 240 179 211 236
13
Ni 566.96 274.08 2643.00 76.74
138.44
Rb 30.31 13.48 58.37 30.21
1.08
Sr 454 335 501 319
8
Y 19.69 11.86 20.92 15.59
1.25
Zr 109.97 65.91 115.13 73.27
6.77
Nb 7.60 4.76 8.61 4.37
0.49
Ba 394 193 560 578
10
La 12.98 7.80 16.22 9.94
0.31
Ce 29.61 18.33 36.63 24.33
0.69
Pr 3.80 2.23 3.97 3.30
0.13
Nd 16.47 9.48 16.87 14.83
0.46
Sm 4.25 2.25 3.32 3.18
0.32
Eu 1.31 0.79 1.12 0.90
0.08
Gd 3.58 2.23 4.33 3.60
0.27
Dy 3.24 2.31 4.16 3.23
0.26
Er 2.24 1.33 2.43 1.65
0.12
Yb 2.34 1.36 2.31 1.31
0.14
Hf 2.53 1.52 3.57 1.67
0.21
Ta 0.42 0.33 0.62 0.30
0.05
Pb 16.08 3.16 15.22 4.61
0.57
Th 2.50 1.49 5.20 1.68
0.17
U 0.93 0.38 3.14 0.55 0.09
148
LCC-2-
01
LCC-2-
02
LCC-2-
04
LCC-2-
05 LCC-2-07
LCC-2-
08
LCC-2-
09
LCC-2-
10 1 S.D.
wt%
SiO2 51.36 51.75 51.52 50.85 50.76 50.62 51.20 50.69 0.26
Al2O3 17.69 18.10 18.09 18.24 17.99 17.81 17.99 18.11 0.11
FeOT 4.93 5.12 5.07 5.16 5.35 5.68 5.22 5.22 0.07
MgO 5.68 5.59 5.46 5.71 5.56 5.64 5.75 5.57 0.05
CaO 10.20 9.85 10.09 10.05 10.12 9.93 10.10 10.18 0.05
Na2O 3.83 3.16 3.52 3.66 3.73 3.58 3.69 3.68 0.14
K2O 0.95 1.03 0.98 0.98 0.97 0.95 0.97 0.96 0.01
TiO2 1.02 1.02 1.03 1.04 1.02 0.98 1.01 0.99 0.02
MnO 0.10 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.01
P2O5 0.20 0.21 0.22 0.22 0.21 0.21 0.21 0.21 0.01
S 0.09 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.003
Cl 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.002
CO2
(ppm) 819 895 1467 1099 993 1111 812 1168 62
H2O 2.34 3.08 3.16 2.26 2.35 2.49 2.29 3.40 0.18
ppm
Li 11.20
8.38
10.31 9.14
1.43
B 6.99
5.19
7.20 6.54
2.70
Sc 27.68
26.26
29.22 29.65
1.37
V 272
208
210 215
13
Ni 201.94
102.16
1352.67 86.05
36.10
Rb 25.59
18.28
18.34 19.00
0.78
Sr 417
412
406 418
8
Y 14.79
15.57
16.08 16.48
0.86
Zr 86.47
93.33
93.24 93.14
5.04
Nb 7.12
6.60
7.19 6.78
0.51
Ba 249
247
250 250
6
La 9.72
9.77
10.06 10.24
0.25
Ce 23.82
22.19
23.03 22.62
0.51
Pr 2.83
2.83
2.84 2.90
0.10
Nd 12.81
12.72
12.97 12.93
0.38
Sm 2.70
2.36
2.96 3.08
0.21
Eu 0.89
0.97
0.95 0.97
0.06
Gd 2.83
2.88
3.06 2.80
0.15
Dy 2.94
2.92
2.92 2.78
0.13
Er 1.55
1.88
1.64 1.78
0.13
Yb 1.10
1.85
1.63 1.22
0.16
Hf 2.07
1.87
1.98 2.30
0.15
Ta 0.36
0.36
0.38 0.38
0.04
Pb 4.16
3.20
3.19 3.74
0.19
Th 1.81
1.55
1.73 1.85
0.11
U 0.65 0.52 0.52 0.54 0.04
149
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